Block polymer processing for mesostructured inorganic oxide materials

ABSTRACT

Mesoscopically ordered, hydrothermally stable metal oxide-block copolymer composite or mesoporous materials are described herein that are formed by using amphiphilic block polymers which act as structure directing agents for the metal oxide in a self-assembling system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of continuation applicationNon-Provisional application Ser. No. 10/426,441 filed on Apr. 30, 2003,now U.S. Pat. No. 7,176,245 which was a continuation of U.S.Non-Provisional application Ser. No. 09/554,259 filed on Dec. 11, 2000now U.S. Pat. No. 6,592,764 which claimed the benefit of PCT/U.S.98/26201, filed Dec. 9, 1998, and also claimed the benefit of U.S.Provisional Application Nos. 60/069,143, filed Dec. 9, 1997, and60/097,012, filed Aug. 18, 1998.

STATEMENT REGARDING FEDERALLY FUNDED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Grant Nos. DMR9257064, DMR 9520971 and DMR 9632716 from the National ScienceFoundation, and Grant No. DAAH-04-96-1-0443 from the United States ArmyResearch Office. The Government has certain rights in this invention.

BACKGROUND OF THE INVENTION

Large pore size molecular sieves are in high demand for reactions orseparations involving large molecules and have been sought after forseveral decades. Due to their low cost, ease of handling, and highresistance to photo induced corrosion, many uses have been proposed formesoporous metal oxide materials, such as SiO₂, particularly in thefields of catalysis, molecular separations, fuel cells, adsorbents,patterned-device development, optoelectronic devices, and chemical andbiological sensors. One such application for these materials is thecatalysis and separation of molecules that are too large to fit in thesmaller 3-5 Å pores of crystalline molecular sieves, providing facileseparation of biomolecules such as enzymes and/or proteins. Suchtechnology would greatly speed processing of biological specimens,eliminating the need for time consuming ultracentrifugation proceduresfor separating proteins. Other applications include supported-enzymebiosensors with high selectivity and antigen expression capabilities.Another application, for mesoporous TiO₂, is photocatalytic watersplitting, which is extremely important for environmentally friendlyenergy generation. There is also tremendous interest in using mesoporousZr₂, Si_(1-x)Al_(x)O_(y), Si_(1x)Ti_(x)O_(y), as acidic catalysts.Mesoporous WO₃ can be used as the support for ruthenium, which currentlyholds the world record for photocatalytic conversion of CH₄ to CH₃OH andH₂. Mesoporous materials with semiconducting frameworks, such as SnO₂and WO₃, can be also used in the construction of fuel cells.

Mesoporous materials in the form of monoliths and films have a broadvariety of applications, particularly as thermally stable low dielectriccoatings, non-linear optical media for optical computing andself-switching circuits, and as host matrices for electrically-activespecies (e.g. conducting and lasing polymers and light emitting diodes).Such materials are of vital interest to the semiconductor andcommunications industries for coating chips, as well as to developoptical computing technology which will require optically transparent,thermally stable films as waveguides and optical switches.

These applications, however, are significantly hindered by the factthat, until this invention, mesoscopically ordered metal oxides couldonly be produced with pore sizes in the range (15-100 Å), and withrelatively poor thermal stability. Many applications of mesoporous metaloxides require both mesoscopic ordering and framework crystallinity.However, these applications have been significantly hindered by the factthat, until this invention, mesoscopically ordered metal oxidesgenerally have relative thin and fragile channel walls.

Since mesoporous molecular sieves, such as the M41 S family ofmaterials, were discovered in 1992, surfactant-templated syntheticprocedures have been extended to include a wide variety of compositionsand conditions for exploiting the structure-directing functions ofelectrostatic and hydrogen-bonding interactions associated withamphiphilic molecules. For example, MCM-41 materials prepared by use ofcationic cetyltrimethylammonium surfactants commonly have d(100)spacings of about 40 Å with uniform pore sizes of 20-30 Å. Cosolventorganic molecules, such as trimethylbenzene (TMB), have been used toexpand the pore size of MCM-41 up to 100 Å, but unfortunately theresulting products possess less resolved XRD diffraction patterns. Thisis particularly the case concerning materials with pore sizes near thehigh-end of this range (ca. 100 Å) for which a single broad diffractionpeak is often observed. Pinnavaia and coworkers, infra, have usednonionic surfactants in neutral aqueous media (S⁰I⁰ synthesis at pH=7)to synthesize worm-like disordered mesoporous silica with somewhatlarger pore sizes of 20-58 Å (the nomenclature S⁰I⁰ or S⁺I⁻ areshorthand notations for describing mesophase synthesis conditions inwhich the nominal charges associated with the surfactant species S andinorganic species I are indicated). Extended thermal treatment duringsynthesis gives expanded pore sizes up to 50 Å; see D. Khushalani, A.Kuperman, G. A. Ozin, Adv. Mater. 7, 842 (1995).

The preparation of films and monolithic silicates using acidic sol-gelprocessing methods is an active research field, and has been studied forseveral decades. Many studies have focused on creating a variety ofhybrid organic-silicate materials, such as Wojcik and KleinÅpolyvinylacetate toughening of TEOS monoliths (Wojcik, Klein; SPIE, PassiveMaterials for Optical Elements II, 2018, 160-166 (1993)) or Lebeau etal's organic-inorganic optical coatings (B. Lebeau, Brasselet, Zyss, C.Sanchez; Chem Mater., 9, 1012-1020 (1997)). The majority of thesestudies use the organic phase to provide toughness or optical propertiesto the homogeneous (non-mesostructured) monolithic composite, and not asa structure-directing agent to produce mesoscopically ordered materials.Attard and coworkers have reported the creation of monoliths with −40 Åpore size, which were synthesized with low molecular weight nonionicsurfactants, but did not comment on their thermal stability ortransparency; see G. S. Attard; J. C. Glyde; C. G. G61tner, C. G. Nature378, 366 (1995). Dabadie et al. have produced mesoporous films withhexagonal or lamellar structure and pore sizes up to 34 Å using cationicsurfactant species as structure-directing species; see Dabadie, Ayral,Guizard, Cot, Lacan; J. Mater Chem., 6, 1789-1794, (1996). However,large pore size (>50 Å) monoliths or films have not been reported, and,prior to our invention, the use of block copolymers asstructure-directing agents has not been previously explored.(after ourinvention, Templin et al. reported using amphiphilic block copolymers asthe structure-directing agents, aluminosilicate mesostructures withlarge ordering lengths (>15 nm); see Templin, M., Franck, A., Chesne, A.D., Leist, H., Zhang, Y., Ulrich, R., Schadler, V., Wiesner, U. Science278, 1795 (Dec. 5, 1997)). For an overview of advanced hybridorganic-silica composites, see Novak's review article, B. Novak; Adv.Mater., 5, 422433 (1993).

While the use of low-molecular weight surfactant species have producedmesostructurally ordered inorganic-organic composites, the resultingmaterials have been in the form of powders, thin films, or opaquemonoliths. Extension of prior art surfactant templating procedures tothe formation of nonsilica mesoporous oxides has met with only limitedsuccess, although these mesoporous metal oxides hold more promise inapplications that involve electron transport and transfer or magneticinteractions. The following mesoporous inorganic oxides have beensynthesized with small mesopore sizes (<4 nm) over the past few years:

-   MnO₂ (Tian, Z., Tong, W., Wang, J., Duan, N., Krishnan, V. V.,    Suib, S. L. Science.-   Al₂O₃ (Bagshaw, S. A., Pinnavaia, T. J. Angew. Chem. Int. Ed. Engl.    35, 1102 (1996)),-   TiO₂ (Antonelli, D. M., Ying, J. Y. Angew. Chem. Int. Ed. Engl. 34,    2014 (1995)),-   Nb₂O₅ (Antonelli, D. M., Ying, J. Y. Chem. Mater. 8, 874 (1996)),-   Ta₂O₅ (Antonelli, D. M., Ying, J. Y. Chem. Mater. 8, 874 (1996)),-   ZrO₂ (Ciesla, U., Schacht, S., Stucky, G. D., Unger, K. K.,    Schuth, F. Angew. Chem. Int. Ed. Engl. 35, 541 (1996)).-   HfO₂ (Liu, P., Liu, J., Sayari, A. Chem. Commun. 557 (1997)), and    reduced Pt (Attard, G. S., Barlett P. N., Coleman N. R. B.,    Elliott J. M., Owen, J. R.,-   Wang, J. H. Science, 278, 838 (1997)).

However these often have only thermally unstable mesostructures; seeUlagappan, N., Rao, C. N. R. Chem Commun. 1685 (1996), and Braun, P. V.,Osenar, P., Stupp, S. I. Nature 380, 325 (1996).

Stucky and co-workers first extended the surfactant templating strategyto the synthesis of non-silica-based mesostructures, mainly metaloxides. Both positively and negatively charged surfactants were used inthe presence of water-soluble inorganic species. It was found that thecharge density matching between the surfactant and the inorganic speciesis very important for the formation of the organic-inorganic mesophases.Unfortunately, most of these non-silica mesostructures are not thermallystable. Pinnavaia and co-workers, supra, used nonionic surfactants tosynthesize mesoporous alumina in neutral aqueous media and suggestedthat the wormhole-disordered mesoporous materials are assembled byhydrogen-bonding interaction of inorganic source with the surfactants.Antonelli and Ying, supra, prepared stable mesoporous titanium oxidewith phosphorus in a framework using a modified sol-gel method, in whichan organometallic precursor was hydrolyzed in the presence ofalkylphosphate surfactants. Mesoporous zirconium oxides were preparedusing long-chain quaternary ammonium, primary amines, and amphotericcocamidopropyl betaine as the structure-directing agents, see Kim, A.,Bruinsma, P., Chen, Y., Wang, L., Liu, J. Chem. Commun. 161 (1997);Pacheco, G., Zhao, E., Garcia, A., Sklyaro, A., Fripiat, J. J. Chem.Commun. 491 (1997); and Pacheco G., Zhao, E., Garcia, A., Skylyarov, A.,Fripiat, J. J. J. Mater. Chem. 8, 219 (1998).

A scaffolding process was also developed by Knowles et al. for thepreparation of mesoporous ZrO₂ (Knowles J. A., Hudson M. J. J. Chem.Soc., Chem. Commun. 2083 (1995)). Porous HfO₂ has been synthesized usingcetyltrimethyllammonium bromine as the structure-directing agent; seeLiu, P., Liu. J., Sayari, A. Chem. Commun. 557 (1997). Suib et al,supra, prepared mixed-valent semiconducting mesoporous maganese oxidewith hexagonal and cubic structures and showed that these materials arecatalytically very active. A ligand-assisted templating approach hasbeen successfully used by Ying and co-workers, supra, for the synthesisof Nb₂O₅ and Ta₂O₅. Covalent bond interaction between inorganic metalspecies and surfactant was utilized in this process to assemble themesostructure. More recently, the surfactant templating strategy hasbeen successfully extended to platinum by Attard, Barlett et al, supra.

For all these mesoporous non-silica oxides (except Pinnavaia's aluminawork, in which copolymers were used to produce mesoporous alumina inneutral aqueous conditions), low-molecular-weight surfactants were usedfor the assembly of the mesostructures, and the resulting mesoporousmaterials generally had small mesopore sizes (<4 nm), and thin (1-3 nm)and fragile frameworks. The channel walls of these mesoporous metaloxides were exclusively amorphous. There have been claims, based solelyon the X-ray diffraction data, of mesoporous ZrO₂ and MnO₂ withcrystalline frameworks; see Bagshaw and Pinnavaia, supra, and Huang, Y.,McCarthy, T. J., Sachtler, W. M. Appl. Catal. A 148, 135 (1996).However, the reported X-ray diffraction patterns cannot exclude thepossibility of phase separation between the mesoporous and crystallinematerials, and therefore their evidence has been inconclusive. Inaddition, most of the syntheses were carried out in aqueous solutionusing metal alkyoxides as inorganic precursors. The large proportion ofwater makes the hydrolysis and condensation of the reactive metalalkyoxides and the subsequent mesostructure assembly extremely difficultto control.

For an overview of the non-silica mesoporous materials prior to thisinvention, see the Sayari and Liu review article, Sayari, A., Liu, P.Microporous Mater. 12, 149 (1997).

There has also been a need for porous inorganic materials with structurefunction on different length scales, for use in areas as diverse aslarge-molecule catalysis, biomolecule separation, the formation ofsemiconductor nanostructure, the development of medical implants and themorphogenesis of skeletal forms. The use of organic templates to controlthe structure of inorganic solid has proven very successful fordesigning porous materials with pore size ranging from angstroms tomicrometers. For example, microporous aluminosilicate andaluminophosphate zeolite-type structures have been templated by organicmoleculars such as amines. Larger mesoporous (20-300 Å) materials havebeen obtained by using long-chain surfactant asstructure-directing-agents. Recent reports illustrate that techniquessuch as surfactant emulsion or latex sphere templating have been used tocreate TiO₂, ZrO₂, SiO₂ structures with pore sizes ranging from 100 nmto 1 _(μ)m. Recently, Nakanishi used a process that combined phaseseparation, solvent exchange with sol-gel chemistry to preparemacroscopic silica structures with random meso and macro-porousstructure; see K. Nakanishi, J. Porous Mater. 4, 67 (1997). Mann andcoworkers used bacterial threads as the templates to synthesize orderedmacrostructures in silica-surfactant mesophases; see Davis, S. L.Burkett, N. H. Mendelson, S. Mann, Nature, 385, 420 (1997)

Researchers have commented on the assembly of inorganic compositesdirected by protein or organic surfactants, but little on the effect ofinorganic salts on the self-assembly of macroscopic silica or calciumcarbonate structures with diatom, coral morphologies; see Davis, S. L.Burkett, N. H. Mendelson, S. Mann, Nature, 385, 420 (1997); A. M.Belcher, X. H. Wu, R. J. Christensen, P. K. Hansma. G. D. Stucky,Nature, 381, 56 (1996); and X. Y. Shen, A. M. Belcher, P. K. Hansma, G.D. Stucky, et al., Bio. Chem., 272, 32472 (1997).

BRIEF SUMMARY OF THE INVENTION

The present invention overcomes the drawbacks of prior efforts toprepare mesoporous materials and mesoscopic structures, and providesheretofore unattainable materials having very desirable and widelyuseful properties. These materials are prepared by using amphiphilicblock copolymer species to act as structure-directing agents for metaloxides in self-assembling systems. Aqueous metal cations partitionwithin the hydrophilic regions of the self-assembled system andassociate with the hydrophilic polymer blocks. Subsequent polymerizationof the metalate precursor species under strongly acidic conditions(e.g., pH 1), produces a densely cross linked, mesoscopically orderedmetal oxide network. Mesoscopic order is imparted by cooperativeself-assembly of the inorganic and amphiphilic species interactingacross their hydrophilic-hydrophobic interface.

By slowly evaporating the aqueous solvent, the composite mesostructurescan be formed into transparent, crack-free films, fibers or monoliths,having two-dimensional hexagonal (p6 mm), cubic (Im3 m), or lamellarmesostructures, depending on choice of the block copolymers. Heating toremove the organic template yields a mesoporous product that isthermally stable in boiling water. Calcination yields mesoporousstructures with high BET surface areas. Unlike traditional sol-gel filmsand monoliths, the mesoscopically ordered silicates described in thisinvention can be produced with high degrees of order in the 100-200 Ålength scale range, extremely large surface areas, low dielectricconstants, large anisotropy, can incorporate very large host molecules,and yet still retain thermal stability and the transparency of fullydensified silicates

In accordance with a further embodiment of this invention, inorganicoxide membranes are synthesized with three-dimension (3-d) meso-macrostructures using simultaneous multiphase assembly. Self-assembly ofpolymerized inorganic oxide species/amphiphilic block copolymers and theconcurrent assembly of highly ordered mesoporous inorganic oxideframeworks are carried out at the interface of a third phase consistingof droplet of strong electrolyte inorganic salts/water solution. Theresult is a 2-d or 3-d macroporous/mesoporous membranes which, withsilica, are coral-like, and can be as large as 4 cm.times.4 cm with athickness that can be adjusted between 10 _(μ)m to several millimeters.The macropore size (0.5-100 _(μ)m) can be controlled by varying theelectrolyte strength of inorganic salts and evaporation rate of thesolvents. Higher electrolyte strength of inorganic salts and fasterevaporation result in a thicker inorganic oxide a framework and largermacropore size. The mesoscopic structure, either 2-d hexagonal (p6 mm,pore size 40-90 Å) or 3-d cubic array, can be controlled by amphiphilicblock copolymer templates. The resulting membranes are thermally stableand have large surface areas up to 1000 m²/g, and pore volume up to 1.1cm³/g. Most importantly, these meso-macroporous coral-like planesprovide excellent access to the mesopore surfaces for catalytic,sorption, catalysis, separation, and sensor arrays, applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a size comparison between two prior art porous inorganicmaterials, Faujasite and MCM-41, and SBA-15, prepared in accordance withthis invention.

FIG. 2 shows powder X-ray diffraction (XRD) patterns of as-synthesizedand calcined mesoporous silica (SBA-15) prepared using the amphiphilicpolyoxyalkylene block copolymer PEO₂₀PPO₇₀PEO₂₀.

FIG. 3 shows scanning electron micrographs (SEM's) (a, b) ofas-synthesized SBA-15 and transmission electron micrographs (TEM's) (c,d) with different orientations of calcined hexagonal mesoporous silicaSBA-15 prepared using the block copolymer PEO₂₀PPO₇₀PEO₂₀.

FIG. 4 shows nitrogen adsorption-desorption isotherm plots (top) andpore size distribution curves (bottom) measured using the adsorptionbranch of the isotherm for calcined mesoporous silica SBA-15 preparedusing the block copolymer PEO₂₀PPO₇₀PEO₂₀ (a, b) without and (c, d) withTMB as an organic additive.

FIG. 5 shows transmission electron micrographs with different pore sizesand silica wall thicknesses for calcined hexagonal mesoporous silicaSBA-15 prepared using the block copolymer PEO₂₀PPO₇₀PEO₂₀. (a) pore sizeof 47 Å, silica wall thickness of 60 Å; (b) pore size of 89 Å, silicawall thickness of 30 Å; (c) pore size of 200 Å; (d) pore size of 260 Å.

FIG. 6 shows powder X-ray diffraction (XRD) patterns of as-synthesizedand calcined mesoporous silica SBA-15.

FIG. 7 shows variation of the d(100) spacing (solid) and pore size(open) for mesoporous hexagonal SBA-15 calcined at 500° C. for 6 h inair (circles) and for mesoporous MCM-41 (squares) as functions of theTMB/amphiphile (copolymer or surfactant) ratio (g/g).

FIG. 8 shows ²⁹Si MAS NMR spectra of as-synthesized silica-copolymermesophase materials; (a) SBA-11 prepared by using Brij C₁₆EO₁₀surfactant; (b) SBA-15 prepared using PEO₂₀PPO₇₀PEO₂₀ block copolymer.

FIG. 9 shows thermogravimetric analysis (TGA) and differential thermalanalysis (DTA) traces for the as-synthesized SBA-15 prepared by usingthe block copolymer PEO₂₀PPO₇₀PEO₂₀.

FIG. 10 shows powder X-ray diffraction (XRD) patterns of (a),as-synthesized and, (b) calcined MCM-41 silica prepared using thecationic surfactant C₁₆H₃₃N(CH₃)₃Br, and (c), calcined MCM-41 afterheating in boiling water for 6 h; Calcined SBA-15 (d, e) prepared byusing the block copolymer PEO₂₀PPO₇₀PEO₂₀ after heating in boiling waterfor (d), 6 h; (e), 24 h.

FIG. 11 shows photographs of transparent SBA-15 silica-copolymermonoliths incorporating (a) 27 wt % and (b) 34 wt % of the PEO-PPO-PEOstructure-directing copolymer PLURONIC F127.

FIG. 12 shows a 200-keV TEM image of a 38 wt % SBA-15 silica-copolymermonolith prepared with PLURONIC F127.

FIG. 13 shows (a) a photograph of a transparent 50-_(μ)m-thick SBA-15silicacopolymer film prepared with PLURONIC P104. (b) an X-raydiffraction pattern of this film showing well resolved peaks that areindexable as (100), (110), (200), and (210) reflections associated withp6 mm hexagonal symmetry in which the one-dimensional axes of theaggregates fie horizontally in the plane of the film.

FIG. 14 shows the predicted variation of optical dielectric constant andrefractive index as a function of silica porosity.

FIG. 15 shows low-angle and wide-angle X-ray diffraction (XRD) patternsof (a, c), as-made zirconium/EO₂₀PO₇₀EO₂₀ composite mesostructure and(b, d) calcined mesoporous ZrO₂. The XRD patterns were obtained with aScintag PADX diffractometer using Cu K.alpha. radiation.

FIG. 16 shows TEM micrographs of 2-dimensional hexagonal mesoporousZrO₂. (a) and (b) are recorded along the [110] and [001] zone axes,respectively. Inset in (b) is the selected-area electron diffractionpattern obtained on the image area. The images were recorded with a 200kV JEOL transmission electron microscope. All samples were calcined at400.degree. C. for 5 hr to remove the block copolymer surfactantspecies.

FIG. 17 shows TEM micrographs of 2-dimensional hexagonal mesoporousTiO₂. (a) and (b) are recorded along the [110] and [001 zone axes,respectively. Inset in (a) is the selected-area electron diffractionpattern obtained on the image area.

FIG. 18 shows TEM micrographs of 2-dimensional hexagonal mesoporous SnO₂(a) and (b) are recorded along the [110] and [001] zone axes,respectively. Inset in (a) is selected-area electron diffraction patternobtained on the image area.

FIG. 19 shows TEM micrographs of 2-dimensional hexagonal mesoporous WO₃(a) and (b) are recorded along the [110] and [001] zone axes,respectively.

FIG. 20 shows TEM micrograph of 2-dimensional hexagonal mesoporousNb₂O₅, recorded along the [001] zone axis. Inset is selected-areaelectron diffraction pattern obtained on the image area.

FIG. 21 shows TEM micrograph of 2-dimensional hexagonal mesoporous Ta₂O₅recorded along the [001] zone axis.

FIG. 22 shows TEM micrographs of disordered hexagonal mesoporous Al₂O₃.

FIG. 23 shows TEM micrograph of 2-dimensional hexagonal mesoporous HfO₂recorded along the [110] zone axis.

FIG. 24 shows TEM micrographs of 2-dimensional hexagonal mesoporousSiAlO₄ recorded along the [001] zone axis.

FIG. 25 shows TEM micrographs of 2-dimensional hexagonal mesoporousSiAlO₃₅. (a) and (b) are recorded along the [110] and [001] zone axes,respectively.

FIG. 26 shows TEM micrograph of 2-dimensional hexagonal mesoporousZrTiO₄ recorded along the [001] zone axes.

FIG. 27 shows (a) Bright field TEM image of a thin slice of themesoporous TiO₂ sample. (b) Dark field image obtained on the same areaof the same TiO₂ sample. The bright spots in the image correspond toTiO₂ nanocrystals.

FIG. 28 shows (a) Bright field TEM image of a thin slice of themesoporous ZrO₂ sample. (b) Dark field image obtained on the same areaof the same Zro₂ sample. The bright spots in the image correspond toZrO₂ nanocrystals.

FIG. 29 shows nitrogen adsorption-desorption isotherms and pore sizedistribution plots (inset) calculated using BJH model from theadsorption branch isotherm for calcined Zro₂. The isotherms weremeasured using a Micromeritics ASAP 2000 system. The samples wereoutgassed overnight at 200° C. before the analyses.

FIG. 30 shows nitrogen adsorption-desorption isotherms (a) and pore sizedistribution plots (b) calculated using BJH model from the adsorptionbranch isotherm for calcined TiO₂. Inset in (b) is the EDX spectrumobtained on the mesoporous samples.

FIG. 31 shows nitrogen adsorption-desorption isotherms and pore sizedistribution plots (lower inset) calculated using BJH model from theadsorption branch isotherm for calined Nb₂O₅. EDX spectrum obtained onthe mesoporous samples is shown in the upper inset.

FIG. 32 shows nitrogen adsorption-desorption isotherms and pore sizedistribution plots (lower inset) calculated using BJH model from theadsorption branch isotherm for calcined Ta₂O₅. EDX spectrum obtained onthe mesoporous samples is shown in the upper inset.

FIG. 33 shows nitrogen adsorption-desorption isotherms and pore sizedistribution plots (inset) calculated using BJH model from theadsorption branch isotherm for calcined Al₂O₃.

FIG. 34 shows nitrogen adsorption-desorption isotherms and pore sizedistribution plots (inset) calculated using BJH model from theadsorption branch isotherm for calcined WO₃.

FIG. 35 shows nitrogen adsorption-desorption isotherms (a) and pore sizedistribution plots (b) calculated using BJH model from the adsorptionbranch isotherm for calcined SiTiO₄.

FIG. 36 shows nitrogen adsorption-desorption isotherms (a) and pore sizedistribution plots (b) calculated using BJH model from the adsorptionbranch isotherm for calcined ZrTiO₄.

FIG. 37 shows low-angle and wide-angle X-ray diffraction (XRD) patternsof (a, c), as-made titanium/EO₂₀BO₇₅ composite cubic mesostructure and(b, d) calcined mesoporous TiO₂.

FIG. 38 shows TEM micrograph of cubic mesoporous TiO₂.

FIG. 39 shows TEM micrograph of cubic mesoporous ZrO₂.

FIG. 40 shows SEM image of calcined mesoporous Al₂O₃ monolithic thickfilm. The image was recorded on JEOL 6300 FX microscope.

FIG. 41 shows scanning electron micrographs (SEM) of (a, b)as-synthesized meso-macro silica membranes prepared by using P123 blockcopolymer (EO₂₀PO₇₀EO₂₀) in NaCl solution after washing out NaCl withde-ionic water; (c), small macropore size silica membrane prepared byadding a little amount ethylene glycol in P123 block copolymer and NaClsolution; (d), silica membrane prepared with fast evaporation by usingP123 block copolymer in NaCl solution. (e), silica membrane with grapevine morphology prepared with high concentration of NaCl; (f), inorganicsalt NaCl crystals co-grown with the silica membrane.

FIG. 42 shows scanning electron micrographs (SEM) of (a, b, c)as-synthesized meso-macro silica membranes prepared by using P123 blockcopolymer (EO₂₀PO₇₀EO₂₀) in (a), KCl; (b), NH₄Cl; (c), NaNO₃ solutionafter washing out inorganic salts with de-ionic water. (d), largemacropore size silica membrane prepared by using P65 block copolymer(EO₂₆PO₃₉EO₂₆) in NaCl solution.

FIG. 43 shows SEM images of as-synthesized silica membranes after washedwith water prepared by (a), using F127 block copolymer (EO₁₀₆PO₇₀OE₁₀₆)in NaCl solution; (b, c, d), using P123 block copolymer in (b), MgSO₄solution; (c), MgCl₂ solution; (d), Na₂SO₄ solution.

FIG. 44 shows powder X-ray diffraction (XRD) patterns of as-synthesizedand calcined mesomacro silica membranes prepared using the amphiphilicpolyoxyalkylene block copolymer (a), P123, EO₂₀PO₇₀OE₂₀; (b), P103,EO₁₇PO₈₅EO₁₇; (c); P65, EO₂₆PO₃₉EO₂₆. The chemical composition of thereaction mixture was 1 g coploymer: 0.017 mol NaCl: 0.01 mol TEOS:4.times.10⁻⁵ mol HCl: 0.72 mol H₂O: 0.33 mol EltOH.

FIG. 45 shows transmission electron micrographs (TEM) (a, b) of calcinedsilica membrane prepared using the block copolymer P123 in NaCl solutionrecorded in (a), (100); (b), (110) zone axes; (c, d) of calcined silicamembrane prepared by adding a little amount of ethylene glycol. TEM weretaken on a 2000 JEOL electron microscope operating at 200 kV.

FIG. 46 shows thermogravimetric analysis (TGA) and differential thermalanalysis (DTA) traces for the as-synthesized meso-macroporous silicamembranes prepared by using the block copolymer P123 (EO₂₀PO₇₀EO₂₀) inNaCl solution, (top) after removal NaCl by washing with water; (bottom),without removal NaCl.

FIG. 47 shows nitrogen adsorption/desorption isotherm plots (a) and poresize distribution curves (b) for mesomacro silica membranes preparedusing block copolymer P123 in NaCl solution without removal inorganicsalt NaCl.

FIG. 48 shows nitrogen adsorption-desorption isotherm plots (top) andpore size distribution curves (bottom) for calcined meso-macro silicamembranes prepared in NaCl solution using different block copolymers.

FIG. 49 shows nitrogen adsorption/desorption isotherm plots (a) and poresize distribution curves (b) for calcined meso-macro silica membranesprepared using block copolymer F127 in NaCl solution.

FIG. 50 shows nitrogen adsorption/desorption isotherm plots (a) and poresize distribution curves (b) for calcined meso-macro silica membranesprepared using non-ionic oligomeric surfactant Brij 76 (C₁₈H₁₇EO₁₀OH) inNaCl solution.

FIG. 51 shows SEM images of (a)-(d), as-synthesized silica membranesprepared by using P123 block copolymer in LiCl solution without washingrecorded at different region, (a), top region; (b) middle region; (c),same (b) with large magnification; (d), bottom region of the membrane.(e)-(h) as-synthesized silica membranes prepared by using P123 blockcopolymer in NiSO₄ solution without washing recorded at differentregion, (a), top region; (b) same (a) with large magnification; (c)bottom region of the membrane; (d), disk-like NiSO₄ crystal.

FIG. 52 shows the change of the compositions of the reaction mixturefunctioned with evaporation time. Change of the concentration in liquidphase of ethanol (open circle); water (solid circle); LiCl (opensquare); SiO₂ (solid square); Intensity ratio for (100) diffraction ofsilica-block copolymer mesophase (open triangle) and for (110)diffraction of LiCl crystal (solid triangle) at d spacing of 3.59 Ådetermined by XRD in solid phase.

FIG. 53 shows a schematic diagram of the simple procedure used toprepare coral-like mesomacro silica membranes.

FIG. 54 shows progressively higher magnifications of a section of ameso-macro silica membrane made in accordance with this invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides a simple and general procedure for the synthesesof ordered large-pore (up to 14 nm) mesoporous metal oxides, includingTiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, Al₂O₃, SiO₂, WO₃, SnO₂, HfO₂ and mixed oxidesSiAlO_(3.5), SiAlO_(5.5), Al₂TiO₅, ZrTIO₄, SiTiO₄. Commerciallyavailable, low-cost, non-toxic, and biodegradable amphiphilicpoly(alkylene oxide) block copolymers can be used as thestructure-directing agents in non-aqueous solutions for organizing thenetwork forming metal species. Preferably the block copolymer is atriblock copolymer in which a hydrophilic poly(alkylene oxide) such aspoly(ethylene oxide (EO_(x)) is linearly covalent with the opposite endsof a hydrophobic poly(alkylene oxide) such as polypropylene) oxide(PO_(y)) or a diblock polymer in which, for example, poly(ethyleneoxide) is linearly covalent with poly(butylene oxide) (BO_(y)). This canvariously be designated as follows:

poly(ethylene oxide)-poly(propylene oxide)-poly(polyethylene oxide)

HO(CH₂CH₂O)_(x)(CH₂CH(CH₃)O)_(y)(CH₂CH—₂O)_(x)H

PEO-PPO-PEO

EO_(x)PO_(y)EO_(x)

or

poly(ethylene oxide)poly(butylene oxide)-poly(polyethylene oxide)

HO(CH₂CH₂O)_(x)(CH₂CH(CH₃CH₂)O)_(y)H

PEO-PBO-PEO

EO_(x)BO_(y)EO_(x)

where x is 5 or greater and y is 30 or greater, with no theoreticalupper limit to either value subject to practical considerations.Alternatively, for particular applications, one can use a reversetriblock copolymer or a star block amphiphilic poly(alkylene oxide blockcopolymer, for example, a star di-block copolymer or a reversed stardi-block copolymer. Inexpensive inorganic salts rather than alkoxides ororganic metal complexes are used as precursors. Both two-dimensionalhexagonal (p6 mm) and cubic (Im3 m) mesostructures can be obtained, aswell as lamellar mesostructures, depending on the choice of the blockcopolymers. Calcination at 400° C. yields mesoporous structures withhigh BET surface area (100-850 m²/g), porosity of 40-65%, large dspacings (60-200 Å), pore sizes of 30-140 Å, and wall thickness of 30-90Å.

These novel mesoporous metal oxides are believed to be formed through amechanism that combines block copolymer self-assembly with chelatingcomplexation of the inorganic metal species. A unique aspect of thesethermally stable mesoporous oxides is their robust inorganic frameworkand thick channel walls, within which a high density of nanocrystallites can be nucleated during calcination without disrupting the mesoscopicordering. In addition, variations of this simple sol-gel process yieldmesoporous oxides with technologically important forms including thinfilms, monoliths and fibers. The nanocrystalline framework, periodiclarge-pore structures, and high versatility of the inexpensive syntheticmethodology make these mesoporous materials an excellent choice forapplications including catalysis, molecular separations, fuel cells,adsorbents, optoelectronic devices, and chemical and biological sensors.For example, due to its low cost, ease of handling, and high resistanceto photoinduced corrosion, one application for mesoporous TiO₂ isphotocatalytic water splitting, which is extremely important forenvironmentally friendly energy generation. There is also tremendousinterest in using mesoporous ZrO₂, Si₁-xAl_(x)O_(y), Si_(1-x)Ti_(x)O_(y)as acidic catalysts. Mesoporous WO₃ can be used as the support forruthenium, which currently holds the world record for photocatalyticconversion of CH₃ to CH₃OH and H₂. Mesoporous materials withsemiconducting frameworks, such as SnO₂ and WO₃, can be also used in theconstruction of fuel cells.

Many applications of mesoporous metal oxides require both mesoscopicordering and framework crystallinity. The mesoporous metal oxides ofthis invention are thermally stable and retain their mesoscopic orderingand structural integrity even after the nucleation of the high densityof nanocrystallites within thick, robust channel walls. Development ofsuch thermally stable, large-pore mesoporous metal oxide materials withnanocrystalline frameworks using lowcost, non-toxic, and biodegradablepolyalkylene oxide block copolymers has enormous potential for a varietyof immediate and future industrial applications.

In practicing this invention, one can use any amphiphilic block polymerhaving substantial hydrophilic and hydrophobic components and can useany inorganic material that can form crown-ether-type complexes withalkylene oxide segments through weak coordination bonds. The inorganicmaterial can be any inorganic compound of a multivalent metal species,such as metal oxides and sulphides, preferably the oxides. The metalspecies preferentially associates with the hydrophilic poly(ethyleneoxide) (PEO) moieties. The resulting complexes then self-assembleaccording to the mesoscopic ordering directed principally by microphaseseparation of the block copolymer species. Subsequent crosslinking andpolymerization of the inorganic species occurs to form themesoscopically ordered inorganic/block-copolymer composites. Theproposed assembly mechanism for these diverse mesoporous metal oxidesuses PEO-metal complexation interactions, in conjunction with (forexample) electrostatic, hydrogen bonding, and van der Waals forces todirect mesostructure formation.

As Indicated above, one can carry out the assembly process innon-aqueous media using metal halides as the inorganic precursors, whicheffectively slows the hydrolysis/condensation rates of the metal speciesand hinders subsequent crystallization. Restrained hydrolysis andcondensation of the inorganic species appears to be important forforming mesophases of most of the non-silica oxides, because of theirstrong tendency to precipitate and crystallize into bulk oxide phasesdirectly in aqueous media.

The procedures of the present invention enable close control of theporosity of the final structure by varying the proportions of PEO andPPO or PBO

and by adding an organic solvent to swell the PPO or PBO.

Because of their low cost, widespread use, and ease of preparation, wewill first describe and exemplify the preparation of mesoporous silica,followed by the preparation of other metal oxides. We will then describethe multiphase assembly of meso-macro membranes, which we will exemplifywith silica membranes.

Mesoporous Silicas

In accordance with this invention, we have synthesized a family of highquality, hydrothermally stable and ultra large pore size mesoporoussilicas by using amphiphilic block copolymers in acidic media. Onemember of the family, to which we have assigned the designation SBA-15,has a highly ordered, two-dimensional hexagonal (p6 mm) honeycomb,hexagonal cage or cubic cage mesostructures. Calcination at 500° C.yields porous structures with high BET surface areas of 690-1040 m²/g,and pore volumes up to 2.5 cm ³/g, ultra large d(100) spacings of74.5-450 Å, pore sizes from 46-500 Å and silica wall thicknesses of31-64 Å. SBA-15 can be readily prepared over a wide range of specificpore sizes and pore wall thicknesses at low temperature (35-80° C.)using a variety of commercially available, low-cost, non-toxic, andbiodegradable amphiphilic block copolymers, including triblockpolyoxyalkylenes, as described below. In general, allmicrophase-separating, domain-partitioning copolymer systems can beconsidered as candidates for the synthesis of such mesostructuredmaterials, depending on solution composition, temperature, processingconditions, etc. The pore size and thickness of the silica wall isselectively controlled by varying the thermal treatment of SBA-15 in thereaction solution and by the addition of cosolvent organic molecules,such as 1,3,5-trimethylbenzene (TMB). The organic template can be easilyremoved by heating at 140° C. for 3 h, yielding the mesoporous SBA-15product, which is thermally stable in boiling water.

Transparent films, fibers, and monolithic materials with mesoscopicorder can also be prepared by a similar process utilizing the samefamily of triblock polyoxyalkylene copolymers, yielding mesoporousstructure in bulk. These materials are similarly synthesized in acidicmedia at low temperatures (20-80° C.), and display a variety ofwell-ordered copolymer phases with mesostructures of about 100-500 Å.They can be processed (e.g., molded) into a variety of bulk shapes,which are also transparent. In addition, it is possible to use polymerprocessing strategies, such as shear alignment, spin casting, and fiberdrawing to induce orientational order in these materials. Aftercalcination at 350° C. these monoliths and films retain theirmacroscopic shape and mesoscopic morphology. To our knowledge, these arethe first reported thermally stable, transparent, monolithic, largepore-size materials with well-ordered mesostructure. Their dielectricconstants can be varied to low values via the Lorentz-Lorenzrelationship by tuning the pore volume fraction from 0.6 to as much as0.86. The fluid sol processability, extraordinary periodic pore and cagestructures, high pore volume fraction and inexpensive synthesis makethem excellent low dielectric materials for inter-level dielectrics(LID) for on-chip interconnects to provide high speed, low dynamic powerdissipation and low cross-talk noise.

To produce the highly ordered, ultra large pore silica mesostructures weadopted an S⁺I⁻X⁻I⁺ synthesis processing strategy. This synthesismethodology is distinctly different from the S⁺I⁻ route (pH>3) used tomake the M41S family of mesoporous materials: the two methods employconditions that are on opposite sides of the isoelectric point ofaqueous silica (pH=2). For example, mesoporous silica SBA-15 can besynthesized using block copolymers, which that have apolyoxyethylene-polyoxypropylene-polyoxyeth-ylene (PEO-PPO-PEO) sequencecentered on a (hydrophobic) polypropylene glycol nucleus terminated bytwo primary hydroxyl groups; see Table 1 The synthesis is carried out inacidic (e.g., HCl, HBr, H₂SO₄, HNO₃, H₃PO₄) media at 35-80° C. usingeither tetraethylortho-silicate (TEOS), tetramethylorthosilicate (TMOS),or tetrapropoxysilane (TPOS) as the silica source.

Hexagonal SBA-15 has a wheat-like macroscopic morphology, a highlyordered (four to seven peaks in the X-ray diffraction pattern),two-dimensional hexagonal (p6 mm) mesostructure, BET surface areas up to1040 m²/g, pore volumes to 2.5 cm³/g, and thick silica walls (31-64 Å)The thick silica walls in particular are different from thethinner-walled MCM-41 mesostructures made with conventional lowmolecular weight cationic surfactants. The pore size and the thicknessof the silica wall can be adjusted by varying the heating temperature(35-140° C.) or heating time (11-72 h) of the SBA-15 in the reactionsolution and by adding organic swelling agents such as1,3,5-trimethylbenzene The thick walls of the hexagonally ordered poresof these materials produce a novel combination of a high degree of bothmesoscopic organization and hydrothermal stability. Based on the aboveproperties, SBA-15 materials have potential applications in catalysis,separations, chemical sensors, and adsorbents.

Transparent films and monoliths have been synthesized with similarPEO-PPO-PEO copolymers as structure-directing agents in an acidicsol-gel reaction. These materials can be synthesized with variousamounts of water, acid, silicate source, and polymer to yield differentmesophase structures depending upon the polymer and processingconditions used. The materials consist of a collection of aggregates ofan organic polymer component, such as the amphiphilic copolymer PLURONICF127, which for a hexagonal array that organizes a polymerized silicamatrix in the interstices between the polymer aggregates. Suchmorphologies are formed by interactions among the block copolymer andthe oligomeric silicate species, and solidified as the silicapolymerizes to form a monolithic structure. The polymer is not stronglyincorporated into the silica walls, as inferred from the remarkably lowtemperature (150° C.) needed to remove the polymer, and supporting ¹Hnuclear magnetic resonance (NMR) relaxation measurements. Thesestructures possess characteristic length scales of 100-200 Å and havevery large domain sizes (>1 _(μ)m), yet retain good transparency. Uponcalcination the monoliths become opaque, though retain their bulk shapeand possess mesoscopically ordered, hexagonally arranged pores (100-200Å diameter), which impart high internal surface areas to the materials(ca. 1000 M²/g).

Synthesis of Highly Mesoscopically Ordered Ultra-Large-Pore andHydrothermally Stable Mesoporous Silica.

Referring to FIGS. 1 a,b,c and d, there is shown, approximately toscale, two prior art inorganic oxide porous structures and the SBA-15produced in accordance with this invention. As shown in FIGS. 1 a and 1b Faujasite, a sub-nanoporous zeolite has a pore size of less than 1 nm.MCM-41, a mesoporous molecular sieve material, shown at FIG. 1 c, has apore size of about 8 nm. In contrast, as shown in FIG. 1 d, SBA-15, theultra large pore mesoporous silica material produced by this invention,has a pore size of about 20 nm, in this particular example.

Mesoporous silica SBA-15 was synthesized at 35-80° C. using ahydrophilic-hydrophobic-hydrophilic PEO-PPO-PEO triblock copolymer asthe structure-directing-agent. 4.0 g of PLURONIC P123 (PE0₂₀PP0₇₀PE0₂₀)was dissolved in 30 g water and 120 g (2 M) HCl solution while stirringat 35° C. To the resulting homogeneous solution 8.50 g TEOS was addedwhile stirring at 35° C. for 22 h. The mixture was then aged at 100° C.without stirring for 24 h. The solid product was filtered, washed, andair-dried at room temperature. Calcination was carried out in air byslowly increasing the temperature (from room temperature to 500° C. over8 h) and heating at 500° C. for 6 h.

X-ray diffraction is an important means for characterizing the SBA-15family of materials. FIGS. 2 a and 2 b show small-angel XRD patterns foras-synthesized and calcined hexagonal mesoporous silica SBA-15 preparedby using the polyoxyalkylene triblock copolymer PE0₂₀PP0₇₀PE0₂₀(PLURONIC P123). The chemical composition of the reaction mixture was 4g of the copolymer: 0.041 M TEOS: 0.24 M HCl: 6.67 M H₂O. The XRDpatterns were acquired on a Scintag PADX diffractometer equipped with aliquid nitrogen cooled germanium solid-state detector using Cu K.alpha.radiation. The X-ray pattern of as-synthesized hexagonal SBA-15 (FIG. 2a) shows four well-resolved peaks that are indexable as (100), (110),(200), and (210) reflections associated with p6 mm hexagonal symmetry.The as-synthesized SBA-15 possesses a high degree of hexagonalmesoscopic organization indicated by three additional weak peaks thatare present in the 2.THETA. range of 1-3.5°, corresponding to the (300),(220), and (310) scattering reflections, respectively. The intense (100)peak reflects a d-spacing of 104 Å, corresponding to a large unit cellparameter (a=120 Å). After calcination in air at 500° C. for 6 h, theXRD pattern (FIG. 2 b) shows that the p6 mm morphology has beenpreserved, although the peaks appear at slightly higher 2.THETA. valueswith d(100)=95.7 Å and a cell parameter (a₀) of 110 Å. Six XRD peaks arestill observed, confirming that hexagonal SBA-15 is thermally stable. Asimilarly high degree of mesoscopic order is observed for hexagonalSBA-15 even after calcination to 850°.

SEM images (FIGS. 3 a, 3 b) reveal that as-synthesized hexagonal SBA-15has a wheat-like morphology with uniform particle sizes of about −80_(μ)m, and that these consist of many rope-like macrostructures. TheSEM's were obtained on a JEOL 6300-F microscope. Calcined hexagonalSBA-15 at 500° C. in air shows a similar particle morphology, reflectingthe thermal stability of the macroscopic shape and structure. TEM images(FIGS. 3 c, 3 d) of calcined SBA-15 with different sample orientationsshow well ordered hexagonal arrays of mesopores (one-dimensionalchannels) and further confirm that SBA-15 has a two-dimensional p6 mmhexagonal structure. The TEM's were acquired using a 2000 JEOL electronmicroscope operating at 200 kV. For the TEM measurements, samples wereprepared by dispersing the powder products as a slurry in acetone andsubsequently deposited and dried on a holey carbon film on a Ni grid.From high-dark contrast in the TEM images, the distance betweenmesopores is estimated to be about 110 Å, in agreement with thatdetermined from XRD data.

Nitrogen adsorption-desorption isotherm plots and the correspondingpore-size distribution curves are shown in FIG. 4 for calcined hexagonalSBA-15 samples that were prepared using the copolymer PEO₂₀PPO₇₀PEO₂₀.The sample corresponding to the measurements shown in FIGS. 4 a and 4 bwas prepared by reaction at 35° C. for 20 h, heating at 100° C. for 48h, and subsequent calcination in air at 500° C., yielding a hexagonalSBA-15 product material with a mean pore size of 89 Å, a pore volume of1.17 cm³/g, and a BET surface area of 850 m²/g. The sample correspondingto the measurements shown in FIGS. 4 c and 4 d was prepared underidentical conditions but additionally used TMB as an organic swellingagent to increase the pore size of the subsequent product material.Using TMB yields hexagonal mesoporous SBA-15 silica with a mean poresize of 260 Å, a pore volume of 2.2 cm³/g, and a BET surface area of 910m² _(μ)g. The isotherms were measured using a Micromeritics ASAP 2000system. Data were analyzed by the BJH (Barrett-Joyner-Halenda) methodusing the Halsey equation for multilayer thickness. The pore sizedistribution curve was obtained from an analysis of the adsorptionbranch of the isotherm. The pore volumes were taken at P/P₀=0.983 signalpoint. Prior to the BET measurements, the samples were pretreated at200° C. overnight on a vacuum line. In both FIGS. 4 a and 4 c, threewell-distinguished regions of the adsorption isotherm are evident: (1)monolayer-multilayer adsorption, (2) capillary condensation, and (3)multilayer adsorption on the outer particle surfaces. In contrast to N2adsorption results for MCM-41 mesoporous silica with pore sizes lessthan 40 Å, a clear type H₁ hysteresis loop in the adsorption-desorptionisotherm is observed for hexagonal SBA-15 and the capillary condensationoccurs at a higher relative pressure (P/P₀-0.75). The approximate poresize calculated using the BJH analysis is significantly smaller than therepeat distance determined by XRD, because the latter includes thethickness of the pore wall. Based on these results, the thickness of thepore wall is estimated to be ca. 31 Å (Table 1) for hexagonal SBA-15prepared using the PEO₂₀PPO₇₀PEO₂₀ copolymer.

Heating as-synthesized SBA-15 in the reaction solution at differenttemperatures (80-140° C.) and for different lengths of time (11 72 h)resulted in a series of structures with different pore sizes (47-89 Å)and different silica wall thicknesses (31-64 Å) (as presented in Table1). The pore sizes and the wall thicknesses determined for hexagonalSBA-15 from TEM images (such as shown in FIGS. 5 a, 5 b) are inagreement with those estimated from X-ray and N₂ adsorptionmeasurements. The walls are substantially thicker than those typical forMCM-41 (commonly 10-15 Å) prepared using alkylammonium ion surfactantspecies as the structure directing-agents. Higher temperatures or longerreaction times result in larger pore sizes and thinner silica walls,which may be caused by the high degree of protonation of the longhydrophilic PEO blocks of the copolymer under the acidic S⁺X⁻I⁺synthesis conditions. EOH moieties are expected to interact stronglywith the silica species and to be closely associated with the inorganicwall. Increasing the reaction temperature results in increasedhydrophobicity of the PEO block group, and therefore on average smallernumbers of the EOH groups that are associated with the silica wall (seebelow) and thus increased pore sizes.

The pore size of hexagonal mesoporous SBA-15 can be increased to.about.300 Å by the addition of cosolvent organic molecules such as1,3,5-trimethylbenzene (TMB). In a typical preparation, 4.0 g ofPLURONIC P123 was dissolved in 30 g water and 120 g (2 M) HCl solutionwith stirring at room temperature. After stirring to dissolve completelythe polymer, 3.0 g TMB was added with stirring for 2 h at 35° C. 8.50 gTEOS was then added to the above homogeneous solution with stirring at35° C. for 22 h. The mixture was then transferred to a Teflon autoclaveand heated at 100-140° C. without stirring for 24 h. The solid productwas subsequently filtered, washed, and air-dried at room temperature.

FIG. 6 shows the typical XRD patterns of hexagonal SBA-15 prepared byadding an organic swelling agent. The chemical composition of thereaction mixture was 4 g of the copolymer: 3 g TMB: 0.041 M TEOS: 0.24 MHCl: 6.67 M H₂O. The X-ray pattern of as-synthesized product (FIG. 6 a)shows three well-resolved peaks with d spacings of 270, 154, and 133 Åat very low angle (20 range of 0.2-1°), which are indexable as (100),(110), and (200) reflections associated with p6 mm hexagonal symmetry.The (210) reflection is too broad to be observed. The intense (100) peakreflects a d-spacing of 270 Å, corresponding to an unusually large unitcell parameter (a=310 Å). After calcination in air at 500° C. for 6 h,the XRD pattern (FIG. 6 b) shows improved resolution and an additionalbroad (210) reflection with d spacing of 100 Å. These results indicatethat hexagonal SBA-15 is thermally stable, despite its unusually largelattice parameter. The N₂ adsorption-desorption results show that thecalcined product has a BET surface area of 910 m ²/g, a pore size of 260Å, and a pore volume of 2.2 cm³/g. TEM images confirm that the calcinedproducts have highly ordered, hexagonal symmetry with unusually largepore sizes (FIGS. 5 c, 5 d).

FIG. 7 shows the change of the pore size and the d-spacing of the XRDd(100) peak as a function of the TMB/copolymer mass ratio for calcinedhexagonal SBA-15. The pore sizes of calcined SBA-15 were measured fromthe adsorption branch of the N₂ adsorption-desorption isotherm curve bythe BJH (Barrette-Joyner-Halenda) method using the Halsey equation formultilayer thickness. The pore size data for the MCM-41 sample weretaken from ref. 4. The chemical compositions of the reaction mixturewere 4 g of the copolymer: x g TMB: 0.041 M TEOS: 0.24 M HCl: 6.67 M H₂Ofor SBA-15 and NaAlO₂: 5.3 C₁₆TMACl: 2.27 TMAOH: 15.9 SiO₂: x g TMB:1450H₂O for the MCM-41 (C₁₆TMACl=cetyltrimethylammonium chloride,TMAOH=tetramethyl-ammonium hydroxide). The ratios used in this studyranged from 0 to 3, with the d(100) spacing and pore size increasingsignificantly, up to 320 Å and 300 Å, respectively, with increasingTMB/copolymer ratio. The increased pore size is accompanied by retentionof the hexagonal mesostructure, with the X-ray diffraction patterns ofeach of these materials exhibiting 3-4 peaks.

To the best of our knowledge, hexagonal SBA-15 has the largest poredimensions thus far demonstrated for mesoscopically ordered poroussolids. As shown in FIG. 7, the d(100) spacing and pore size of calcinedMCM-41 prepared by using cationic surfactant species can also beincreased, but compared to SBA-15, the change is much less. In addition,although MCM-41 pore sizes of ca. 100 Å can be achieved by addingauxiliary organic species (e.g., TMB), the resulting materials havesignificantly reduced mesostructural order. The XRD diffraction patternsfor such materials are substantially less resolved, and TEM micrographsreveal less ordering, indicating that the materials possess lowerdegrees of mesoscopic order. This is particularly the case near thehigh-end of this size range (−100 Å) for which a broad single peak isoften observed. These materials also tend to suffer from poor thermalstability as well, unless additional treatment with well TEOS (whichreduces the pore size) is carried out. From our results, a family ofhighly ordered mesoporous SBA-15 silica can be synthesized with largeuniform and controllable pore sizes (from 89-500 Å) by using PEO-PPO-PEOcopolymer species as amphiphilic structure-directing agents, augmentedby the use of organic swelling agents in the reaction mixture. The poresize for hexagonal SBA-15 determined by TEM images (FIGS. 5 c, 5 d) isin agreement with that established from separate N₂ adsorptionmeasurements.

Magic-Angle Spinning ²⁹Si NMR spectra (FIG. 8) of as-synthesizedhexagonal SBA-15 show three broad peaks at 92, 99, and 109 ppm,corresponding to Q², Q³, and Q⁴ silica species, respectively. From therelative peak areas, the ratios of these species are established to beQ²:Q³:Q⁴=0.07:0.78:1. These results indicate that hexagonal SBA-15possesses a somewhat less condensed, but similarly locally disordered,silica framework compared to MCM-41.

TGA and DTA analyses (FIG. 9) of hexagonal SBA-15 prepared usingPEO₂₀PPO₇₀PEO₂₀ show total weight losses of 58 wt % apparentlyconsisting of two apparent processes: one at 80° C. (measured using TGA)yields a 12 wt % loss, accompanied by an endothermic DTA peak due todesorption of water, followed by a second 46 wt % weight loss at 145° C.with an exothermic DTA peak due to desorption of the organic copolymer.A Netzsch Thermoanalyzer STA 409 was used for thermal analysis of thesolid products, simultaneously performing TGA and DTA with heating ratesof 5 Kmin-¹ in air.

The desorption temperature of the large block copolymer (−150° C.) ismuch lower than that of cationic surfactants (−360° C.), so that theorganic copolymer species can be completely removed and collectedwithout decomposition by heating SBA-15 in an oven (air) at 140° C. for3 h. (The possibility to recover and reuse the relatively expensivetriblock copolymer structure-directing species is an important economicconsideration and benefit to these materials.) It should be noted thatthe pure block copolymer PEO₂₀PPO₇₀PEO₂₀ decomposes at 270° C., which issubstantially lower than that of cationic surfactants (−360° C.) duringcalcination. For comparison, the TGA of the copolymer PEO₂₀PPO₇₀PEO₂₀impregnated in SiO₂ gel shows that the copolymer can be desorbed at 190°C., which is −50° C. higher than required for hexagonal SBA-15. Removalof the organic species from as-synthesized SBA-15 at these relativelylow temperatures (e.g., 140° C.) suggests the absence of strongelectrostatic or covalent interactions between the copolymer species andthe polymerized silica wall, together with facile mass transport throughthe pores. The possibility to recover and reuse the relatively expensivetriblock copolymer structure-directing species is an important economicconsideration and advantage of these materials.

Hexagonal SBA-15 can be synthesized over a range of copolymerconcentrations from 2-6 wt % and temperatures from 35-800° C.Concentrations of the block copolymer higher than 6 wt % yielded onlysilica gel or no precipitation of silica, while lower copolymerconcentrations produced only dense amorphous silica. At roomtemperature, only amorphous silica powder or products with poormesoscopic order can be obtained, and higher temperatures (>80° C.)yield silica gel. Like TEOS, tetramethylorthosilicate (TMOS) andtetrapropoxysilane (TPOS) can also be used as the silica sources for thepreparation of hexagonal SBA-15.

SBA-15 can be formed in acid media (pH<1) using HCl, HBr, Hl, HNO₃,H₂SO₄, or H₃PO₄. Concentrations of HCl (pH 2-6) above the isoelectricpoint of silica (pH 2) produce no precipitation or yield unorderedsilica gel. In neutral solution (pH 7), only disordered or amorphoussilica is obtained. We also measured the precipitation time (t) of thesilica as a function of the concentration of HCl and Cl⁻ The [Cl⁻]concentration was varied by adding extra NaCl, while keeping the H⁺concentration constant. From these measurements, log (t) is observed toincrease linearly with log C (where C is the concentration of HCl orCl⁻). Slopes of 0.31 for [Cl⁻] and 0.62 for HCl indicate that Cl⁻influences the synthesis of SBA-15 to a lesser extent than does H⁺.Based on these results, we propose that the structure-directed assemblyof SBA-15 by the polyoxyalkylene block copolymer in acid media occurs bya S⁺X⁻I⁺ pathway. While both the EO and PO groups of the copolymer arepositively charged in acidic media, the PO groups are expected todisplay more hydrophobicity upon heating to 35-80° C., therebyincreasing the tendency for mesoscopic ordering to occur. The protonatedpolyoxyalkylene (S⁺, the anionic inorganic (X⁻) bonding, S⁺X⁻, and thepositive silica species (I⁺) are cooperatively assembled by hydrogenbonding interaction forces. Assembly of the surfactant and inorganicspecies, followed by condensation of silica species, results in theformation of hexagonal SBA-15 mesophase silica. At high pH values (2-7),the absence of sufficiently strong electrostatic or hydrogen bondinginteractions leads to the formation of amorphous or disordered silica.

One of the limitations of calcined MCM-41 materials prepared withoutadditional treatment with TEOS is their poor hydrothermal stability. Asshown in FIG. 10, both as-synthesized and calcined (500° C. for 6 h)MCM-41, prepared with C₁₈H₃₃N(CH₃ ⁻ )₃Br as previously described, showwell resolved hexagonal XRD patterns (FIGS. 10 a, 10 b). However, afterheating in boiling water for 6 h, the structure of calcined MCM-41 isdestroyed and the material becomes amorphous, as evidenced by theabsence of XRD scattering reflections in FIG. 10 c. By contrast, all ofthe calcined hexagonal SBA-15 samples prepared using the PEO-PPO-PEOblock copolymers are stable after heating in boiling water for 24 hunder otherwise identical conditions. For calcined hexagonal SBA-15prepared by using the PEO₂₀PPO₇₀PEO₂₀ copolymer and after calcination inair at 500° C. and subsequent heating in boiling water for 6 h, the(210) reflection becomes broader, the (300), (220), and (310) peaksbecome weaker, while the (100) peak is still observed with similarintensity (FIG. 10 d). After heating in boiling water for 24 h, theintensity of the (100) Bragg peak (FIG. 10 e) is still unchanged.Nitrogen BET adsorption isotherm measurements carried out after suchhydrothermal treatment shows that the monodispersity of the pore size,surface area, and pore volume are retained. The results confirm thatcalcined hexagonal SBA-15 silica is significantly more hydrothermallystable than calcined hexagonal MCM-41 silica, most likely because SBA-15has a thicker silica wall. This is an improved one-step alternative totwo-step post-synthesis treatments that use tetraethylorthosilicate(TEOS) to stabilize mesoporous MCM-41 by reforming and structuring theinorganic wall with additional silica.

Preparation of Mesoscopically Ordered Silica-Copolymer Monoliths andFilms.

A typical preparation of monolithic silica-copolymer mesostructures isoutlined below. A series of samples was made with varying amounts ofPLURONIC F127 PEO₁₀₀PPO₆₅PEO₁₀₀ triblock copolymer, while holding otherprocessing conditions constant. A calculated amount of a 20 wt %EtOH/PLURONIC F127 solution (between 0.7 and 3.5 ml) is transferred intoa 30 ml vial. 0.72 ml of an acidic solution of HCl (pH 1.5) is added tothe polymer solution while stirring, followed by addition of 1.0 ml oftetraethylorthosilicate (TEOS). The solution is stirred untilhomogeneous, and allowed to gel uncovered under ambient conditions.After gelation (−2 days) the samples are covered for 2 weeks at roomtemperature. At the end of this period the gels have shrunk, yet done souniformly to retain the shape of the container. Further research hasshown that addition of a small amount of3-glycidoxypropyltrimethoxysilan-e can prevent shrinkage. The cover isremoved and the materials are dried at room temperature to eliminateexcess solvent. The F127 series materials produced are transparent up to38 wt % polymer, after which the polymer macro-phase separates creatinga white opaque material. FIGS. 11 a and 11 b show optical photographs oftwo of the monoliths produced. These monoliths were produced using a 2:1ratio of water to TEOS at pH 1.4 and room temperature, with aging forapproximately 1 month. Note the high degree of transparency and only onecrack in the 34 wt % sample. Subsequent research has allowed us toproduce crack-free monoliths by varying the aging time and temperature.The monoliths pictured are approximately 3-mm thick; although thickermonoliths can be produced, the aging time for these samples increasessignificantly to eliminate cracking.

These monoliths were analyzed using XRD, TEM, and NIVIR to determinemesostructural morphology, as well as the mechanism of the structureformation. The F127 polymer series above showed an aggregation point ofroughly 25 Wt % F127, below which the polymer was disordered andhomogeneously dispersed within the matrix and above which aggregation ofthe polymers led to silica-copolymer mesophases. The copolymer weightpercents required to produce specific phases vary depending upon theexact conditions and copolymer used, however this example may beconsidered representative, though by no means all inclusive, of theresults observed.

XRD patterns of powdered samples obtained from the monoliths show asingle diffraction peak with increasing intensity for increasing polymerconcentration with a maximum at 38 wt %. Below 27 wt % F127, no XRDintensity is observed. The d(100) peak is centered at 112 Å for 27-34 wt% and increases to 120 Å for the 38 wt % sample. The change in thelocation of the peak is due to phase changes in the material, asobserved by TEM and NMR. TEM reveals well ordered silica-copolymermesophases in the samples with higher copolymer concentration, such asthe lamellar phase in the 38 wt % sample shown in FIG. 12. The imageshows that the material has an extremely well ordered lamellarmesoscopic structure with a repeat distance of .about.105 nm. The imageregion is 990.times.1200 nm. The large background stripes are artifactsproduced by the microtome cutting process and are otherwise unrelated tothe morphology of the material. Lower concentrations of copolymerproduced hexagonal, gyroid, or micellar phases with spacings of about110 Å. The domain sizes for these structures is quite large, well over 1_(μ)m² for the lamellar phase, which makes it surprising that only oneXRD peak is observed, although others have shown that single XRDpatterns do not always imply poorly ordered materials (F. Schuth). Below27 wt % no mesostructural ordering is observed.

NMR spectroscopy was utilized to provide information aboutcopolymer-silicate interactions on the molecular level. ¹HT_(ip)relaxation and two-dimensional ²⁹Si—¹H and ¹³C—¹H heteronuclearcorrelation NMR experiments reveal that the polymer is rigidlyincorporated in the silicate at 11 wt % and begins to microphaseseparate at 20 wt %. At 27 wt % the PEO and PPO are 80% separated fromthe silicate, and at 38 wt % the PPO is fully separated (>10 Å) from thematrix. This indicates that a phase change has occurred in progressingfrom copolymer concentrations of 27 to 34 wt % in the samples, wheresome PPO-²⁹Si correlation intensity is still observed. Some PEO wasobserved to be associated with the matrix at all concentrations,implying that the polymerizing silica and PEO blocks are compatible.This suggests that the material is produced by polymerization ofsilicate oligomers that selectively swell the PEO block of the compositemesostructure.

It is possible to use this chemistry and processing to produce thinSBA-15 silica-copolymer films by either spin-, drop-, or dip-casting.Such films can serve as robust permeable coatings for use in separationor chemical sensing applications or as host matrices for optically orelectrically active guest molecules for use in optoelectronic devices.FIG. 13 shows a photograph and X-ray diffraction pattern of an opticallytransparent hexagonal SBA-15 polymer film formed by drop-casting thereaction solution (2 ml TEOS, 0.6 ml H₂O, 0.80 g PLURONIC P104, 1 mldimethylformamide) onto a glass slide and drying at room temperature.The film is 50-_(μ)m thick, crack-free and transparent. The X-raydiffraction pattern of this film shows well resolved peaks that areindexable as (100), (110), (200), and (210) reflections associated withp6 mm hexagonal symmetry in which the one-dimensional axes of the ca.200 Å aggregates are highly ordered horizontally in the plane of thefilm.

High quality films can be produced generally as follows. A mixture of 5ml tetraethylorthosilicate and 0.75-3.0 ml H₂O (pH=1.4) is stirred forapproximately 30 min or until the silicate has hydrolyzed sufficientlyto become miscible with water and thereby form a homogeneous solution.An appropriate amount (generally between 1040 wt %) of block copolymer,such as PLURONIC P104polyethyleneoxide-polypropyleneoxide-polyethyleneoxide copolymer, isdissolved in the solution. An additive such as ethanol, dimethylformamide, or tetrahydrofuran can be added to vary the viscosity andcoating properties. The mixture is allowed to age, then is dip-, drop-,or spin-coated onto a glass or Si wafer substrate. Thin films withvariable thicknesses can also be produced using spin coating.

The XRD patterns confirm that these thin films have highly orderedhexagonal (p6 mm), cubic (1 m3 m), or 3-d hexagonal (p6₃/mmc)mesostructures. They are highly ordered and can easily be shear aligned.BET measurements show that the thin films have narrow pore sizedistributions, pore sizes of 20-120 Å, pore volumes up to 1.7 cm³/g andBET surface areas up to −1500 m²/g. SEM images of these thin films showa uniformly flat surface. The thickness of the films can be adjustedfrom 100 nm-1 mm by varying the concentration of the solution, agingtime and coating time.

The examples shown above use PEO₂₀PPO₇₀PEO₂₀ copolymer species as thestructure-directing agents. Highly ordered, ultra large pore size SBA-15materials can also be synthesized by using PEO-PPO-PEO block copolymerswith different ratios of EO to PO and without adding supplementalorganic swelling agents, such as TMB. Table 1 summarizes thephysicochemical properties of mesoporous silica prepared by usingtriblock and reverse triblock copolymers. The d(100)-spacings from X-raydiffraction measurements can be in the range of 74.5-118 Å, with poresizes of 46-100 Å established by N₂ adsorption measurements. The EO/POratio and intramolecular distribution and sizes of the correspondingblocks affects the formation of SBA-15. A lower EO/PO ratio with asymmetric triblock PEO-PPO-PEO copolymer architecture favors theformation of p6 mm hexagonal SBA-15. For example, PLURONIC L121,PEO₅PPO₇₀PEO₅ at low concentrations (0.5-1 wt %) forms hexagonal SBA-15,while use of higher concentrations of this copolymer (2-5 wt %) leads toan unstable lamellar mesostructured silica phase. Higher EO/PO ratios ofthe block copolymer, e.g. PEO₁₀₀PPO₃₉PEO₁₀₀ or PEO₈₀PPO₃₀PEO₈₀, yieldcubic SBA-15 silica, including an Im3 m morphology. These cubicmesophase materials yield large 54-80 Å mesoscopically ordered pores andhigh BET surface areas (up to 1000 m²/g). Hexagonal mesoporous silicaSBA-15 can also be synthesized by using reverse PPO-PEO-PPO triblockcopolymer configuration, for example, PEO₁₉PPO₃₃PEO₁₉.

In general, any microphase-separating, domain-partitioning copolymerarchitecture can be considered promising for the synthesis of suchmesostructured materials, according to the specifications imposed byprocessing conditions and ultimately the product properties desired.Additionally, cubic (Pm3 m) and hexagonal (p6 mm) mesostructures can beformed by using Brij 56, C₁₆H₃₃(OCH₂CH₂)₁₀OH(C₁₆EO₁₀) surfactantspecies, with the pore sizes controllable from 25-40 Å and BET surfaceareas up to 1070 m²/g. Brij 76 (C₁₈EO₁₀) yields the three-dimensionalhexagonal (P6₃/mmc) and two-dimensional hexagonal (p6 mm) mesostructureswith similar pore sizes and surface areas; see Table 2.

Films and monoliths can be produced with several variations of thesolution conditions and/or sol-gel parameters, such as the ratio ofwater to TEOS, aging time, acidity, additives, temperature, and choicesof copolymer or nonionic surfactants. Materials for specificapplications can be formulated by appropriate modification of theseparameters. Heat treatment after gelation can also produce hardermaterials that are less likely to crack.

We have found that silica-surfactant mesophases and MCM-41-typemesoporous materials can be aligned using liquid crystal processingstrategies, including imposition of magnetic, shear, or electric fields.Similarly, polymer processing of the silica-copolymer composites isexpected to be equally advantageous for producing aligned ultra largemesopore hydrothermally spH materials. For example, it should bepossible to induce orientational ordering of the silica-copolymercomposites and resultant mesoporous materials by applying shear to thesol-gel/copolymer system as it dries. Concerning variations onprocessing SBA-15-copolymer thin films (0.1-100 _(μ)m), use of shearalignment strategies, including spin-casting and dip-casting (i.e.,drawing a vertical coverslip from a reservoir of the reaction solution),have been shown to induce larger degrees of orientational order thanprovided by drop-cast preparations. Moreover, guest molecules such asconducting or optically active organic species can be introduced to thereaction solution(s) and incorporated into the silica-copolymermonoliths, films or powders prior to or during processing. We havedemonstrated the efficacy of this for the inclusion of conductingpolymer moieties, such as poly(3,4-ethylenedioxythiophene) in SBA-15silica-copolymer monoliths and spin-, drop-, and dip-cast films.

Methods currently available for the preparation of inorganic-organicmesophases or mesoscopically ordered porous materials typically involveone of five pathways that rely on Coulombic or hydrogen-bondinginteractions, represented by the shorthand notations S⁺I⁻, S⁺X⁻I⁺, S⁻I⁺,S⁻X⁺I⁺, or S⁰I⁰. The most popular route used in syntheses of mesoporousmaterials has been the S⁺I⁻ approach in basic media, but the S⁻I⁺ andS⁻X^(+I−) syntheses generally yield unstable non-silica based mesoporousmaterials. Furthermore, the surfactants used as the structure-directingagents in these cases (e.g., alkylammonium, alkylamine) are expensiveand/or environmentally noxious. The S⁰I⁰ synthesis route generallyyields disordered or worm-like mesoporous solids due to the absence ofstrong electrostatic or hydrogen bonding interactions. The materials andsynthesis method described here are less expensive, non-toxic, andconsiderably more versatile than the cases described above. They can beused to tune material properties, such as mesoscopic ordering, poresize, hydrothermal stability, monolith shape, orientational alignment,and compatibility with a wide range of guest molecules to asignificantly greater extent than possible with the currentstate-of-the-art.

The ultra large mesopores in calcined SBA-15 materials provide newopportunities in chromatographic separations of large molecules, such asproteins, enzymes, or polymers. In addition, these materials havepromise for new applications in environmental remediation, such as theclean up of polycyclic aromatics, porphyrins, other large organics, andheavy metals from process streams or soils. These properties can beenhanced and tailored by functionalizing molecular moieties along theinorganic walls to provide chemical as well as size selectivespecificity of adsorption interactions.

To the best of our knowledge there have been no reports ofmesoscopically ordered silica monoliths or films with largecharacteristic structural length scales (>50 Å). The large dimensions ofthe inorganic-copolymer aggregates and large pore sizes of the compositeor mesoporous materials detailed herein are superior to conventionalmesoporous solids due to their thermal stability, transparency,monolithic form, and ability to incorporate large guest molecules.SBA-15 mesoporous silica also has distinct advantages over dense silica,particularly for applications requiring a lower dielectric constantmaterial. SBA-15 has much lower density, long range mesoscopic order andpossibilities for obtaining materials with high degrees of structuralanisotropy, compared to dense silica. The improvements substantiallyexceed those provided by MCM-type materials, as discussed earlier. Thishas attractive implications for the development of low dielectricconstant materials, particularly for reducing the capacitance ofinterconnects, which are among the most severely limiting factors inimproving integrated and optical circuit performance. As shown in FIG.14, the quest for materials with dielectric constants significantlybelow 2 appears to be well within reach; calcined SBA-15 materials havebeen prepared with porosities of 0.6-0.86, which lead to calculatedoptical dielectric constants of 1.1-1.4. One can produce alignedmorphologies or structures with unconnected spherical cavities toeliminate transverse channel connectivities, which are undesirable fordielectric materials applications.

Use of block copolymers with a hydrophobic core also produces the uniqueability to stabilize hydrophobic guest molecules that would nototherwise be compatible with the hydrophilic sol-gel reaction, such assome optically active dyes and polymers. Before now all optical moietiesincorporated into sol-gel materials were either water soluble or had tobe chemically grafted onto a compatible polymer. The inclusion of ahydrophobic region within our silicates, yet still smaller then opticalwavelengths, allows an entirely new area of monoliths and coatings to bedeveloped using hydrophobic dyes and optically active organics whileretaining optical transparency. Furthermore, inclusion of guestconducting or optically active species, such as polymers and/or metalnanoparticles, in the pores can create quantum-effect materials. Thecontrollability of the SBA-15 pore sizes, inorganic wall composition,organic composition, and guest species composition permit the properties(e.g., optoelectronic, mechanical, thermal, etc.) to be tuned over anenormous range. Indeed, sequential introduction of guest species, forexample a conducting polymer coating on the interior of the inorganicwall, followed by a second polymer or metal/semiconductor species in thepore center, could lead to the first mesoscopically ordered arrays ofnanosized coaxial quantum wires.

Generalized Block Copolymer Syntheses of Mesoporous Metal Oxides

Mesoporous metal oxides were synthesized at 30-70° C. usingpoly(alkylene oxide) block copolymersHO(CH₂CH₂₀)_(x)(CH₂-2CH(CH₃)O)₂y(CH₂CH₂₀)_(x)H(EO_(x)—PO_(y)—EO—_(x)) orHO(CH₂CH₂₀)₂x(CH₂CH(CH₃CH₂)O)_(y)H(EO_(x),—BO_(y)) block copolymers asthe structure-directing agents. In a typical synthesis, 1 g ofpoly(alkylene oxide) block copolymer was dissolved in 10 g of ethanol(EtOH). To this solution, 0.01 mole of the inorganic chloride precursorwas added with vigorous stirring. The resulting sol solution was gelledin an open petri dish at 40-60° C. in air. The aging time differs fordifferent inorganic systems. Alternatively, the sol solution can be usedto prepare thin films by dip coating. The as-made bulk samples or thinfilms were then calcined at 400° C. for 5 hours to remove the blockcopolymer surfactants. For the Al and Si. ₁-xAl_(x) systems, calcinationwas carried out at 600° C. for 4 hr. For WO₃, calcination at 300° C. issufficient to yield ordered mesoporous oxides.

X-ray diffraction (XRD) is an important technique for characterizingthese metal oxide mesostructures. Table 3 summarizes the syntheticconditions, including the inorganic precursors and aging temperaturesand times for the mesostructured inorganic/copolymer composites (beforecalcination) using EO₂₀PO₇₀EO₂₀ as the structure-directing agent. Abroad array of mesostructured composites have been successfullyprepared, covering the first-, second- and third-row transition metalsand some main group elements as well. The ordering lengths shown inTable 3 correspond to the largest d value observed from the low-angleXRD patterns; it ranges from 70 to 160 Å for the different systems.High-order low-angle diffractions are also observed for most of thesesystems. Quantitative elemental chemical analysis suggests that theframeworks of these mesostructured composites are made up ofmetal-oxygen-chlorine networks.

Upon calcination, mesoporous TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, Al₂O₃, WO.₃,SiO₂, SnO₂, HfO₂, and mixed oxides Si₁-xTi_(x)y, Zr₁1-xTi_(x)O_(y),Al₁-xTi_(x)O_(y), Si₁-xAl._(x)O_(y) are obtained. X-ray diffraction,transmission and scanning electron microscopy imaging (TEM & SEM), andnitrogen adsorption/desorption are three crucial techniques forcharacterization of these materials. Table 4 summaries the analysisresults, including the ordering length, pore size, wall thickness, wallstructure, porosity and Brunauer-Emmet-Teller (BET) surface area.

FIG. 15 shows typical XRD patterns for mesostructured zirconium oxidesprepared using EO₂₀PO₇₀EO₂₀ as the structure-directing agent before andafter calcination. The as-made zirconium inorganic/polymer mesostructure(FIG. 15 a) shows three diffraction peaks with d=115, 65, and 59 Å.After calcination, the diffraction peaks appear at higher 20 angles withd=106, 60, and 53 Å (FIG. 15 b). Both sets of diffraction peaks can beindexed as the (100), (110), and (200) reflections from 2-dimensionalhexagonal mesostructures with lattice constants ₀=132 and 122 Å,respectively. Similar XRD results are obtained in other mesoporous metaloxides. The ordering lengths of these mesoporous metal oxides (Table 4)are substantially larger than those of materials previously reported.

Thermogravimetric experiments indicate that the block copolymer iscompletely removed upon calcination at 400° C. The appearance oflow-angle diffraction peaks indicates that mesoscopic order is preservedin the calcined metal oxide materials. This is confirmed by TEM imagesobtained from mesoporous samples. As examples, FIGS. 16-26 show TEMimages of mesoporous ZrO₂, TiO₂, SnO₂, WO₃, Nb₂O₅, Ta₂O₅, Al₂O₃, HfO₂,SiTiO₄, SiAlO_(3.5), and ZrTiO₄ recorded along the [110] and [100] zoneaxes of the 2-dimensional hexagonal mesostructures. In each case,ordered large channels are clearly observed to be arranged in hexagonalarrays. The pore/channel walls are continuous and have thicknesses of−3.5-9 nm. They are substantially thicker than those typical of metaloxides prepared using alkyammonium ion surfactant species as thestructure-directing agents. In addition, energy dispersive X-rayspectroscopy (EDX) measurements made on the calcined samples show theexpected primary metal element signals with trace of Cl signal, whichconfirms that the inorganic walls consist predominantly of metal-oxygennetworks.

Furthermore, selected area electron diffraction patterns (ED) recordedon mesoporous ZrO₂, TiO₂, SnO₂, and WO₃ show that the walls of thesematerials are made up of nanocrystalline oxides that show characteristicdiffuse electron diffraction rings (FIGS. 16-18 and 20 insets).Wide-angle X-ray diffraction studies of calcined samples also clearlyshow broad peaks that can be indexed according to the correspondingoxide crystalline phase. FIG. 15 d shows a wide-angle diffractionpattern for the calcined Zro₂ sample. The sizes of the nanocrystals inthe calcined materials are estimated to be .about.2 nm using theScherrer formula. In addition, bright-field and dark-field (BF/DF) TEMimaging were employed to study the distribution of these nanocrystals.FIGS. 27 and 28 show such images recorded on same area of one thinmesoporous TiO₂ and ZrO₂ sample. As can be seen in the dark field image(FIGS. 27 b, 28 b), the oxide nanocrystals (.about.2 nm) are uniformlyembedded in a continuous amorphous inorganic matrix to formsemicrystalline wall structures. This is the first time that thecombination of electron diffraction, X-ray diffraction, and brightfield/dark field TEM imaging has been used to conclusively demonstratethat our mesoporous metal oxides have nanocrystalline framework.

FIGS. 29-36 show BET isotherms that are representative of mesoporoushexagonal ZrO₂, TiO₂, Nb₂O₅, Ta₂O₅, Al₂O₃, WO₃, SiTiO₄, and ZrTiO₄.Barrett-Joyner-Halenda (BJH) analyses show that the calcined hexagonalmesoporous metal oxides exhibit pore sizes of 35-140 Å, BET surfaceareas of 100-850 M²g, and porosities of 40-60%. The pore sizes are againsubstantially larger than the previous reported values. For most of theisotherms obtained on these metal oxides, three well-distinguishedregions of the adsorption isotherm are evident: (1) monolayer-multilayer adsorption, (2) capillary condensation, and (3) multilayeradsorption on the outer particle surfaces. In contrast to N₂ adsorptionresults obtained for mesoporous metal oxides prepared usinglow-molecular-weight surfactants with pore sizes less than 4 nm, largehysteresis loops that resemble typical H₁- and H₂-type isotherms areobserved for these mesoporous metal oxides.

The foregoing examples used EO₂₀PO₇₀EO₂₀ copolymer species as thestructure-directing agent. Mesoporous metal oxides with othermesostructures can be synthesized by using EO_(x)-PO_(y)-EO_(-x) orEO_(x)-BO_(y) block copolymers with different ratios of EO to PO or BO.For example, when EO₇₅BO₂₅ copolymer is used as the structure-directingagent, mesoporous TiO₂ with cubic mesostructure can be prepared. FIG. 37shows typical XRD patterns for mesostructured titanium oxides preparedusing EO₇₅BO₇₀ as the structure-directing agent, before and aftercalcination. The as-made titanium inorganic/polymer mesostructure (FIG.35 a) shows six diffraction peaks with d=100, 70, 58, 44, 41, 25 Å,which can be indexed as (110), (200), (211), (310), (222), (440)reflections of an Im3 m mesophase. After calcination, the diffractionpeaks appear at higher 20 angles with d=76, 53, and 43 Å (FIG. 35 b).These diffraction peaks can be indexed as the (110), (200), and (211)reflections from Im3 m mesostructures. The cubic mesostructure isconfirmed by the TEM imaging (FIGS. 38 39).

Films and monoliths (FIG. 40) can be produced by varying such syntheticconditions as the solvent, the ratio of inorganic/polymer, agingtemperature, aging time, humidity, and choice of the block copolymer.Liquids that are common solvents for inorganic precursors and the blockcopolymers (e.g. methanol, ethanol, propanol, butanol) can be usedduring the synthesis. The temperature, the amount of water added, andthe pH can adjusted to control formation of the mesostructures.Materials for specific applications can be formulated by appropriatemodification of these parameters.

The advantages and improvements over existing practice can be summarizedas follows:

(1) Robust, thick channel walls (35-90 Å) which give enhanced thermaland chemical stabilities.

(2) Very large pore sizes (3.5-14 nm)

(3) Use of low-cost inorganic precursors

(4) Versatile synthetic methodology using non-aqueous media that can begenerally applied to vastly different compositions, among whichmesoporous SnO₂, WO₃, and mixed oxides SiTiO₄, ZrTiO₄, Al₂TiO₅ aresynthesized for the first time.

(5) For the first time, conclusive demonstration of thenanocrystallinity of the framework in mesoporous Zro₂, TiO₂, SnO₂, WO₃using XRD, ED and BFIDF TEM imaging

(6) Mesoporous metal oxides with various physical properties includingsemiconducting, low dielectric-constant, high dielectric-constant, andnegative thermal expansion.

Crystallization of inorganic species during cooperativeinorganic/organic self-assembly can lead to macroscopic phase separationof the inorganic and organic components. This is because crystallizationenergies often dominate the interaction energies that stabilize theinorganic-organic interface, thereby disrupting the establishment ofmesostructural order. This is particular the case for non-lamellarphases. In the present invention, this situation is successfullycircumvented by using conditions that initially produce a mesoscopicallyordered material with an amorphous inorganic wall structure (FIGS. 15 cand 35 c) within which a high density of nanocrystals can subsequentlybe nucleated upon calcination. The thick wall and the noncrystallizedinorganic matrix prevent this partially crystalline structure fromcollapsing by effectively sustaining the local strain caused by thenucleation of the nanocrystals. The coexistence of mesoscopic orderingand framework nanocrystallinity is extremely important for catalysis,sensor, and optoelectronic applications.

To the best of our knowledge, there has been no previous report ofmesoporous metal oxide synthesis with such simplicity and versatility.The formation, with such unprecedented simplicity and generality, oflarge-pore mesoscopically ordered metal oxides suggests that the samegeneral inorganic/block polymer assembly mechanisms may be operating. Infact, it is well documented that alkylene oxide segments can formcrown-ether type complexes with many inorganic ions, through weakcoordination bonds. The multivalent metal species (M) can associatepreferentially with the hydrophilic PEO moieties, as indicated in Scheme1, because of their different binding capabilities with poly(ethyleneoxide) (PEO) and poly(propylene oxide) (PPO). The resulting complexesthen self-assemble according to the mesoscopic ordering directedprincipally by the microphase separation of the block copolymer species,and subsequently cross-link and polymerize (Scheme 1) to form themesoscopically ordered inorganic/polymer composites. 1

The proposed assembly mechanism for these diverse mesoporous metaloxides uses PEO-metal chelating interactions in conjunction withelectrostatics, van der Waals forces, etc., to direct mesostructureformation.

A unique feature of the current synthetic methodology is use ofinorganic precursors in non-aqueous media. Because of the lowerelectronegativies of the transition metals compared to silicon, theiralkoxides are much more reactive towards nucleophilic reactions such ashydrolysis and condensation. There has been some work on thenonhydrolytic sol-gel chemistry of inorganic oxides, a non-hydrolyticroute involving carbon-oxygen bond cleavage instead of the metal-oxygenbond which has a general tendency to delay crystallization of the metaloxides, a very important for the first step of our inorganic-copolymercooperative self-assembly process. In addition, the hydrolytic route tometal oxides often leads to difficulties in controlling stoichiometryand homogeneity. Homogeneity depends on the rate of homocondensation(i.e. formation of M-O-M and M′-O-M′) versus the rate ofheterocondensation, which can be hardly controlled in the hydrolyticprocess because of the different reactivities of the various precursorstowards hydrolysis and condensation. However, in principle, thenon-hydrolytic process should favor the formation of homogeneous binaryoxides from different metal precursors because of the decreaseddifference in hydrolysis and condensation rates for different inorganicsources in non-aqueous media. This has been successfully demonstrated inthe mesoporous mixed oxides syntheses using the methods of thisinvention.

This utilization of block copolymer self-assembly in conjunction withchelating complexation for inorganic/organic cooperative assembly in thenon-aqueous media make it possible to synthesize mesoporous materialswith vastly different compositions exemplified in Table 4.

Cooperative Multiphase Assembly of Meso-Macro Silica Membranes

Here we describe a novel procedure for the synthesis of artificial coralsilica membranes with 3-d meso-macro structures. This process utilizesmultiphase media while including microphase separation blockcopolymer/silica composite and macrophase separation between strongelectrolytes and the composite in a single step. We find that strongelectrolytes such as NaCl, LiCl, KCl, NH₄Cl, KNO₃, or even transitionmetal cationic salts such as NiSO₄, can be used to prepare meso-macrosilica membranes that are formed at the interface of droplets of theseinorganic salt solution. It is well known that in nature, macroscopicordered silica structure such as diatom and coral are grown through aprotein modified process in the ocean environments that are rich ininorganic salts such as NaCl. The process used in this study may besignificant in understanding the formation of diatom and coral in naturewhich also can be considered as a 3phase media process: the environmentof the cell, the cell membrane and the aqueous media within the cell.

The silica membranes (size—4 cm×4 cm, thickness—5 mm) with 3-dmeso-macro silica network structures that we have prepared show orientedcontinuous rope, tyroid, and grape vine or dish pinwheel, and gyroid,morphologies depended on the electrolyte strength of the inorganic saltsor amphiphilic block copolymer templates. The macropore size (0.5-100_(μ)m) can be controlled by inorganic salts and evaporation rate of thesolvent. The mesoscopic structures can be highly ordered 2-d honeycomb(pore size 40-90 Å) or 3-d cubic packing, and controlled by theamphiphilic block copolymer templates. These artificial coral meso-macrosilica membranes are thermally stable and exhibit a large surface areasup to 1000 cm² _(μ)g and pore volumes up to 1.5 cm³g.

The silica membranes were prepared by the use of two-step sol-gelchemistry. First oligomeric silica sol-gel was obtained bypre-hydrolysizing of tetraethoxysiliane (TEOS) in ethanol solution by anacid-catalyzed process. Second, the oligomeric silica sol-gel was addedinto a mixture solution of poly(ethylene oxide)-block-ploy(propyleneoxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer andinorganic salts in water and ethanol. The final composition of thismixture was range of 1 TEOS: (6.8-34)×10⁻³ copolymer 0.51-3.0 inorganicsalt: 18-65H²O: 0.002-0.04 HCl: 11-50 EtOH. The silica membranes with3-d meso-macro structures were obtained after drying at roomtemperature, washing with water to remove the inorganic salts, andcalcination to completely remove the organic block copolymer.

In a typical synthesis, 2.08 g TEOS (Aldrich) were added to 5 g ethanol,0.4 g water and 0.4 g (0.1 M) of HCl solution with stirring at roomtemperature for 0.5 h, then heated at 70° C. without stirring for 1 h.After cooling to room temperature, 1 g EO₂0PO₇0EO. 20 (PLURONIC P123,Aldrich/BASF, average molecular weight 5800), 1 g NaCl, 10 g ethanol and10 g water were added to this solution with stirring at room temperaturefor 1 h. The resultant solution was transferred into an open petri dish,allowed to evaporate at room temperature. After complete drying, thesolid membrane was removed from the dish, 20 g water added and thenheated in a sealed container at 100° C. for 3 days to dissolved theinorganic salts. After cooling to room temperature, the solid silicamembranes were washed with de-ionic water and dried at room temperature.The as-synthesized silica membranes were calcined at 500° C. for 6 h inair to completely remove all organic block copolymers.

FIG. 41 shows several representative scanning electron microscope (SEM)images, obtained on a JEOL 6300-F microscope, of the silica membranesand inorganic salt (NaCl) crystal co-grown with the membranes by sol-gelchemistry. The silica membranes prepared from NaCl solution show 3-dmacroscopic network structures and a coral-like morphology (FIG. 41 a).The reticular 3-d network (thickness of −1 _(μ)m) of the silica membraneis made up of continuous rope-like silica which exhibits highlymesoscopic ordering (see below). The silica membranes can be as large as−4 cm×4 cm depended on the size of the container that is used. Thethickness of the silica membranes can be varied from 10 _(μ)m to 5 mm.

As shown in FIG. 41 b, the whole silica membrane shows similar localmacroscopic structure that is not long-range ordering. The averagemacropore size of the silica membranes is about −2 _(μ)m (.±.0.4) (FIG.41 a) and can be varied from −0.5 _(μ)m to −100 _(μ)m by changing theevaporation rate or the electrolyte strength of the inorganic salts. Forexample, when a small amount of ethylene glycol is added into thesol-gel solution to slow the evaporation rate, a small macropore size(−0.5 _(μ)m) is obtained as shown in FIG. 41 c. Of interest is findingthat when the evaporation rate is low, the thickness of the silicanetwork is decreased several hundreds nanometer as shown in FIG. 41 c.When the evaporation rate is high, the macropore size of the silicamembranes can be as large as −10 _(μ)m, the framework thickness isincreased (as shown in FIG. 41 d) and the macroscopic structure of thesilica membranes is changed to a 2-d honey comb channel structure.

The electrolyte strength of the inorganic salts also can be used tocontrol the macropore size. By using stronger electrolytes, for example,MgSO₄, the macropore size can be as much as −20 _(μ)m. In addition, themorphology of the silica membrane can be modified through changing theconcentration of inorganic salts. Low concentrations of the inorganicsalts result in an inhomogeneous silica membrane. While highconcentrations, result in the grape vine morphology that makes up thesilica membrane as shown in FIG. 41 e.

The morphologies of the inorganic salt crystals are also affected by theorganic block copolymer. For example, without the amphiphilic blockcopolymer, cubic crystals of NaCl as large as −100 _(μ)m can be grown inthe solution of water and ethanol, however, in the presence of thesurfactant under our synthesis conditions, most NaCl crystals show anacicular (−1 _(μ)m in diameter) morphology (FIG. 41 f, with a length ofas much as 1 cm. When NiSO₄ is used as the inorganic salts in oursynthesis condition, a disk-like morphology of NiSO₄ crystal is observedat the bottom of the silica membranes. This suggests that thecrystallization of the inorganic salts can also be directed by blockcopolymers.

Besides NaCl, other inorganic salts such as LiCl, KCl, NH₄Cl, Na₂SO₄,MgSO₄, NiSO₄, MgCl₃, chiral NaClO₃, and organic acids such as, malicacid, can be used to form the silica membranes. FIG. 42 shows severalrepresentative scanning electron microscope (SEM) images of themeso-macroporous silica membranes prepared by using block copolymer P123(a-c), or P65 (d) in different inorganic salt solutions. The morphologyof the silica membranes is dependent on the electrolyte strength of theinorganic salts. For example, when LiCl, KCl, and NH₄Cl are used, withelectrolyte strengths comparable to that for NaCl, a similar coral-likemorphologies (FIGS. 42 a, b, c) are observed, although the networkmorphology of the silica membranes is somewhat different. However, whenthe inorganic salts with stronger electrolyte strengths such as Na₂SO₄,MgSO₄, are used in the synthesis, the macroscopic structures consistsilica networks made up of toroid, pinwheel, dish, and gyroidmorphologies (FIG. 43).

The macroscopic structure is also affected by the block copolymer. Whenhigher aver-age molecular weight block copolymers such as PLURONIC F127(EO₁₀₆PO₇₀EO₁₀₆) is used, cubic morphology is observed by SEM (FIG. 43a). This morphology results from silica grown around cubic NaClcrystals, suggesting a macroscopic inorganic crystal templating processfor the mesoporous silica growth. When block copolymers such as PLURONICP65 (E0₂₆PO₃₉EO₂₆) is used, the silica membrane with large macroporesize is obtained (FIG. 42 d).

The mesoscopic ordering in these silica membranes formed by thecooperative self-assembly of inorganic silica species/amphiphilic blockcopolymer is mainly controlled by the block copolymer while can becharacterized by the low-angle X-ray diffraction patterns (FIG. 44) andtransmission electron microscope (TEM) (FIG. 45). The XRD patterns ofFIG. 44 were acquired on a Scintag PADX diffractometer using Cu Karadiation. For the TEM of FIG. 45 measurements, the sample was preparedby dispersing the powder products as a slurry in acetone andsubsequently deposited and dried on a hole carbon film on a Cu grid. Asshown in FIG. 44 a, the coral-like silica membranes synthesized by usingP123 triblock copolymer after removal of NaCl by washing, shows atypical hexagonal (p6 mm) XRD pattern for mesoporous materials with fourdiffraction peaks (a=118 Å), which is similar to that of SBA-15described above. After calcination at 500° C. in air for 6 h, thefour-peak XRD pattern is also observed and the intensity of thediffraction peaks is increased, suggesting that the p6 mm mesoscopicordering is preserved and thermally stable, although the peaks appear atslightly larger 20 values, with a=111 Å. The cell parameters ofmesoscopic ordering on the silica membranes can be varied by usingdifferent triblock copolymers. For example, a=101 Å for Plunroin P103(EO₁₇PO₈₅EO₁₇) (FIG. 44 b) and a=73.5 Å for Plunronic P65 (E0₂₆PO₃₉EO₂₆)(FIG. 44 c), these materials have 2-d hexagonal (p6 mm) mesoscopichighly ordered structures.

These results suggest that the presence of the inorganic salts such asNaCl does not greatly effect the cooperative self-assembly of blockcopolymer/silica to form highly ordered mesostructure. FIGS. 45 a,b showTEM images of calcined silica membranes prepared by using P123 blockcopolymer in NaCl solution at different orientations, confirming thatsilica network of the membranes is made up of a 2-d p6 mm hexagonalmesostructure, with a well-ordered hexagonal array and one-dimensionalchannel structure. TEM images (FIGS. 45 c, d) of the silica membraneswith small macropore size (.about.0.5 _(μ)m from SEM) prepared by addinga small amount of ethylene glycol show that the rope-like networks ofthe silica membranes is made up of loop-like mesoscopic silica withoriented 1-d channel arrays parallel to the long axis. These rope-likesilicas form a 3-d network macroporous structure. It should be notedthat when higher molecular weight block copolymer F127 is used as themesoscopic structure-directing agents, a silica membrane with cubicmesostructure (a=217 Å) can be obtained, based on XRD and TEM results.

SEM images of the silica membranes after calcination at 500° C. in airshow that the coral-like macrostructure is retained, demonstrating thatthe coral-like meso-macro silica membranes prepared with inorganic saltsare thermally stable. Thermal gravimetric and differential thermalanalyses (TGA and DTA) (FIG. 46) in air of the silica membranes preparedby using P123 block coploymer in NaCl solution after removal of theinorganic salts, show total weight losses of only 24 weight % (FIG. 46top). A Netzsch Thermoanalyzer STA 409 was used for thermal analysis ofthe solid products, simultaneously performing TGA and DTA with heatingrates of 5 Kmin.⁻¹ in air. At 100° C. TGA registers a 18 weight % lossaccompanied by an endothermic DTA peak caused from desorption of water,this is followed by a 6 weight % TGA loss at 190° C. which coincideswith an exothermic DTA peak associated with decomposition of the organicblock coploymer. By comparison, the silica membranes obtained withoutremoved the inorganic salts show total weight losses of 50 weight %(FIG. 46 bottom). At 100° C. TGA registers a 4 weight % loss fromphysical adsorption, of water, followed by a 46 weight % TGA loss at200° C. from decomposition of the organic block copolymer.

The above observations confirm that the interaction between silicaspecies and block copolymer species is weak, and after washing withwater 84 weight % of the block copolymer in the silica membranes isremoved. After washing by water and without calcination, these silicamembranes already show similar nitrogen sorption behavior to that forcalcined silica membranes, (FIGS. 47 a, b) so that after washing, bothmacroporous (−0.2 _(μ)m) and mesoporous (60 Å) channels are alreadyaccessible. The isotherms of FIG. 47 were measured using a MicromeriticsASAP 2000 system. Data were calculated by using the BdB (Broekhoff andde Boer) model. The pore size distribution curve was obtained from ananalysis of the adsorption branch of the isotherm. The pore volume wastaken at P/P₀=0.985 signal point. The BET sample was pretreated at 200°C. overnight on the vacuum line.

The representative nitrogen adsorption/desorption isotherms and thecorresponding pore size distribution calculated by using Broekhoff andde Boer's model are shown in FIG. 48. The isotherms of FIG. 48. Theisotherms were measured using a Micromeritics ASAP 2000 system. Datawere calculated by using the BdB (Broekhoff and de Boer) model. The poresize distribution curve was obtained from an analysis of the adsorptionbranch of the isotherm. The pore volume was taken at P/P₀=0.985 signalpoint. The BET sample was pre-treated at 200° C. overnight on the vacuumline. The coral-like silica membranes prepared using P123 blockcopolymers in a NaCl solution show a typical isotherm (type IV) ofcylindrical channel mesoporous materials with H,-type hysteresis, andexhibit a narrow pore size distribution at the mean value of 84 Å. Thismaterial has a Brunauer-Emmett-Teller (BET) surface area of 660 m²/9,and a pore volume of 1.1 cm³/g. The mesoscopic pore size of thesilica-membranes prepared in NaCl solution depended on the amphiphilicblock copolymer, for example, the materials prepared by using P103 andP65 show similar isotherms and exhibit pore sizes of 77 and 48 Å, BETsurface areas of 720 and 930 m²/g, and pore volumes of 1.12 and 0.99 cm³_(μ)g respectively (FIG. 48). When large molecular weight F127 blockcopolymer is used as the templates, the silica membrane with cubicmesoscopic structure shows the isotherms with a large H₂-type hysteresis(FIG. 49 a) much different with that for hexagonal mesoscopic arraysilica membranes and does not fits to cylinders model by using BdB modelto calculate the pore size distribution. (FIG. 49 b) However, usingspheres model, it shows quite narrow pore size distribution at a mean of10.5 nm, and exhibit a BET surface area of 1003 m²/g, pore volume of 0.8cm³/g (FIG. 49 b). The silica membranes prepared by using nonionicoligomeric surfactant C₁₆H₃₃EO₁₀ also high BET surface area of 710 m²/gand pore volume of 0.64 cm³/g, but slight smaller a mean pore size of3.6 nm (FIG. 50 a,b).

In order to understand the formation of the coral-like meso-macro silicamembranes, we have carefully investigated the macroscopic structures indifferent areas (FIG. 51) of the as-made silica membranes prior towashing. As shown in FIGS. 51 a-d, without washing out the inorganicsalt (LiCl) the macroscopic coral-like structures of the membrane havebeen already formed in the middle region of the silica membrane. On theother hand, the image recorded in the top region of the silica membraneis quite different than that from the middle region and show disorderedpillow windows that have similar average macro-window size compared thatin the middle region. These results suggest that the silica membranegrown at the air interface is different than that water interface. FIG.51 d shows the SEM image of the silica membrane prepared by LiClrecorded at the bottom region, suggesting that the mosaic-like inorganicsalt LiCl crystals, which are confined by XRD and chemical analysis, areformed in the bottom of the silica membranes. The shape of thepillow-like LiCl crystals is somewhat similar to the fenestratedmorphology observed at the top region of the silica membrane. SEM imagesof the silica membrane prepared by using NiS04 as the inorganic saltrecorded on the top, middle, bottom regions of the membrane are shown inFIGS. 51 e-h. Without washing out the inorganic salt (NiSO₄) (FIGS. 51e,f) SEM images reveal a disk-like window morphology at the top of themembrane, while inside this window, a coral-like morphology can be seen(FIG. 46 f). However, at the bottom of the membrane, grape vine-likesilica macrostructures with disk-like inorganic salt-NiSO₄ crystals areobserved (FIGS. 51 g, h). The size of disk-like NiSO₄ crystals is thesame as the window size of the silica membrane at the top. These resultsare consist with initial phase separation between the coral-like silicamacrostructure and inorganic salts, followed by formation of the silicamacrostructure above the inorganic salts.

In order to further confirm the formation of the materials, weinvestigate the change of composition as a function of the evaporationtime (FIG. 52). The chemical composition of the starting reactionmixture was 1 g P123 block coploymer 0.01 mol TEOS: 1 g LiCl: 4×10⁻⁵ molHCl: 0.55 mol H₂O: 0.33 mol ETOH. As shown in FIG. 52, in the beginning,the concentration (weight %) of ethanol is decreased rapidly, and theconcentration of water and SiO₂ and inorganic salt LiCl are increasedsince a large amount of ethanol is evaporated. After about 3 h,silica-block copolymer gel starts to form, in liquid phase, theconcentration of silica is rapidly decreased and the concentration ofLiCl is rapidly increased. When the silica mesostructure is formed asdetermined by XRD, almost all the ethanol has evaporated (in liquidphase, a concentration lower than 1%) and only a trace amount of silicais found in the liquid phase, suggesting that the silica/organic blockcopolymer composition has been already solidified at this time at theinterface with salt water. When the concentration of salt LiCl is nearsaturation concentration (45%), the crystallization of the inorganicsalt LiCl occurs. At this time, the formation of mesostructured silicahas been almost completed. These results further indicate that themacroscopic silica structure is formed first at the interface ofinorganic salt water, and sequentially, when the solution of theinorganic salt reaches saturation concentrations, crystal of inorganicsalts are formed in the bottom of the membrane.

Based on above results, we postulate that macroscopic silica structureis formed around a droplet of inorganic salt solution as illustrated inScheme A (FIG. 53). Ethanol is first evaporated, then, water. As theinorganic salt solution becomes more concentrated, two domains areformed, one a water-rich domain, where most inorganic salt is located,another a water-poor domain, where silica and block copolymercompositions are located. The formation of two domains results intri-phase separation, a droplet of inorganic salt solution phaseseparated by silica-block copolymer gel. The droplet of the solutionserves as a template for the growth of silica-block copolymercomposites. Once the macrostructure is rigidified, the inorganic saltsolution approaches to the bottom of the container progressively. Thecooperative self-assembly of silica/block copolymer occurs at theinterface of the droplet, and results in coral-like mesomacroscopicsilica structure. On the other hand, when the silica is formed at theinterface of air and salt water, the droplet of the salt solutionbecomes flatters, resulting in the fenestrated membrane at the top.

Referring to FIG. 54, progressively higher magnifications are shown of asection of a meso-macro silica membrane made in accordance with thisinvention. The membrane is shown in FIG. 54 a which has a macroporestructure, as shown in FIG. 54 b. However the walls defining themacropores have a mesoporous structure.

In summary, artificial coral silica membranes with 3-d meso-macrostructures have been synthesized by a novel process of an acidiccatalyzed silica sol-gel chemistry in the present of inorganic salts.Inorganic salts play an important role on the formation of meso-macrosilica membranes that are grown at the interface of a droplet ofinorganic salt solution. The results are of general important forunderstanding multiphase processes such as the formation of diatomscoral silica structures in nature. The silica membranes (size—4 cm×4 cm,thickness—5 mm) with 3-d meso-macro silica network structures showoriented continuous rope, toroid, and grape vine, or dish, pinwheel,gyroid, and cubic cage morphologies depending on the electrolytestrength of the inorganic salts or amphiphilic block copolymertemplates. The macropore size (0.5-100 _(μ)m) can be controlled byinorganic salts and the evaporation rate of the solvent. The mesoscopicstructures can be highly ordered 2-d honeycomb (pore size 40-90 Å) or3-d cubic packing and are controlled by the amphiphilic block copolymertemplates. The coral-like mesomacro silica membranes are thermallystable and exhibit large surface areas (to 1000 cm²/g) and pore volume(to 1.1 cm³/g). We anticipate that these new process ceramics materialwith structure and design on multiple length scales will have manyapplications in the areas, including separation, sorption, medicalimplant, catalysis, and sensor array applications.

The example shown above in forming meso-macro silica membranes usedPLURONIC P123 block copolymer, EO₂₀PO₇₀EO₂₀ as the template to controlmesoscopic ordering of the silica membranes. Besides P123, othersurfactants can also be used in the synthesis. For example, one coulduse:

(1) a diblock copolymer, poly(ethylene oxide)block-poly(propyleneoxide); poly(ethylene oxide)block-poly(butylene oxide) (Dow Company);B50-6600, BL50-1500;

(2), a triblock copolymer, poly(ethylene oxide)block-poly(propyleneoxide)-block poly(ethylene oxide); (BASF) poly(ethyleneoxide)-block-poly(butylene oxide)-block poly(ethylene oxide) (DowCompany); such as PLURONIC L64, L121, L122, P65, P85, P103, P104, P123,PF20, PF40, PF80, F68, F88, F98, F 108, F 127;(3) a reversed triblock copolymer PLURONIC 25R8, 25R4, 25R2(4) a star di-block copolymer (BASF), TETRONIC 901, 904, 908; and(5) a reversed star di-block copolymer TETRONIC 90R1, 90R4, 90R8.

The inorganic salts can be electrolyte, such as KCl, NaCl, LiCl, NH₄Cl,MgCl, MgSO₄, KNO₃, NaClO₃, Na₂SO₄, NiSO₄, CoCl₂, water organic acid,such as DL tartaric acid, citric acid, malic acid. We claim thatdissolvable alkali salts, alkaline earth salts, transition metal,sulfate, nitrate, halide, chlorate, per chlorate.

The preparation of meso-macro silica membrane are emulsion chemistrylatex sphere template; phase separation and solvent exchanged; inorganicsalts templating which was developed by ourselves here. This discoveryshould have great signification for understanding the formation of thediatom and coral in nature, The macromesoporous materials would havemany applications in the areas of sorption, catalysis, separation,sensor arrays, optoelectionic devices. The materials and synthesismethod described here are very versatile in that they can be used formany fields of application and for synthesis of any inorganic-surfactantcomposites, for example, aluminophosphate-based, TiO₂, ZrO₂, Al₂O₃,Nb₂O₅, Ta₂O₅, Cr₂O₃, Fe₂O₃, ZrTiO₄, Al₂SiO₅, HfO₂, meso-macroporoussilica membranes. These materials would have many applications onsorption, catalysis, separation, sensor arrays, optoelectionic devices.

1. A method of forming a mesoscopically structured material comprisingthe step of combining an amphiphilic block copolymer with an inorganicspecies in a solvent, wherein the block copolymer and the inorganicspecies are assembled and then the assembled inorganic species arepolymerized to form a mesoscopically structured inorganic-organiccomposite, wherein said inorganic species combined with said blockcopolymer is a precursor inorganic species and said assembled inorganicspecies are hydrolyzed inorganic species, and wherein said inorganicspecies is a mixture comprising at least two ofM(OR)s_(s-t-u-v-w-y)R′_(t)R″_(u)R′″_(v)R″″_(w)R′″″_(y), and/or MX_(S)wherein: M is at least one atom other than carbon, hydrogen, oxygen, ornitrogen; S>=1; R, R′, R″, R′″, R″″, and R′″″ are organic moieties;while 0 >=s, t, u, v, w, y >=6; s-t-u-v-w-y>=1; and X is a halogen atom.2. The method of claim 1, wherein said inorganic species is selectedfrom the group consisting of AlCl₃/SiCl₄, ZrCl₄/TiCl₄, AlCl₃/TiCl₄,SiCl₄/TiCl₄, ZrCl₄/WCl₆, SnCl₄/InCl₃.
 3. The method of claim 1, whereinsaid mesoscopically structured inorganic-organic composite hasmacroscopic orientational order.
 4. The method of claim 1, wherein saidmesoscopically structured inorganic-organic composite has a framework inwhich there is located nanocrystallites.
 5. The method of claim 1,wherein said mesoscopically structured inorganic-organic composite is inthe form of (a) a powder, (b) a film, (c) a fiber, or (d) a monolith. 6.The method of claim 1, wherein said amphiphilic block copolymer and saidinorganic species are combined under non-hydrolytic conditions.
 7. Themethod of claim 1, wherein said amphiphilic block copolymer and saidinorganic species are combined under non-aqueous conditions.
 8. Themethod of claim 1, wherein said block copolymer and inorganic speciesare assembled and polymerized within an aligning field to form themesoscopically structured inorganic-organic composite which has amacroscopic orientational order.
 9. The method of claim 1, wherein saidcombined block copolymer and inorganic species are processed to induceorientational ordering before the assembled inorganic species arepolymerized to form the mesoscopically structured inorganic-organiccomposite.
 10. The method of claim 1, wherein said block copolymer andinorganic species are assembled and polymerized in the presence ofelectrically responsive molecules or optically responsive molecules toform the mesoscopically structured inorganic-organic composite.
 11. Themethod of claim 1, including the step, after assembly of the blockcopolymer and the inorganic species and polymerization of the assembledinorganic species, of calcining said mesoscopically structuredinorganic-organic composite to form a mesoscopically structuredmaterial.
 12. The method of claim 1, including the step, afterself-assembly of the block copolymer and the inorganic species andpolymerization of the assembled inorganic species, of solvent extractingsaid mesoscopically structured inorganic-organic composite to form amesoscopically structured material.
 13. The method of claim 1, includingthe step, after self-assembly of the block copolymer and the inorganicspecies and polymerization of the assembled inorganic species, ofremoving the block copolymer from said mesoscopically structuredinorganic-organic composite to form a mesoscopically structuredmaterial.
 14. The method of claim 1, wherein said mesoscopicallystructured inorganic-organic composite is functionalized to impartresponsiveness in at least one property including an optoelectronicproperty, a mechanical property, a thermal property, an opticalproperty, a separation property, or a reaction property to form amulti-functional mesoscopically structured inorganic-organic composite.15. A method of making any of(a) a fuel cell material, (b) anopto-electronic material, (c) a quantum-effect material, or (d) amedical implant, from a mesoscopically structured inorganic-organiccomposite or a mesoporous inorganic oxide material which are formed bycombining an amphiphilic block copolymer with an inorganic species in asolvent, wherein the block copolymer and the inorganic species areassembled and then the assembled inorganic species are polymerized toform said mesoscopically structured inorganic-organic composite.
 16. Themethod of claim 15 in which mesoscopically structured material is formedby the following steps: placing the amphiphilic block copolymer in anaqueous solution of inorganic salt; combining the aqueous solutioncontaining the block copolymer with the inorganic species to form amultiphase medium that enables microphase separation of inorganicspecies and the block copolymer, thereby forming an inorganic-blockcopolymer composite, wherein the block copolymer enables macrophaseseparation of the inorganic-block copolymer composite and the aqueoussolution of inorganic salt; polymerizing the inorganic species to form ameso-macrostructured inorganic-organic composite; removing the blockcopolymer and aqueous solution from said meso-macrostructuredinorganic-organic composite to form said mesoscopically structuredmaterial.
 17. A mesoscopically structured material that was formed bycombining an amphiphilic block copolymer with an inorganic species in asolvent, wherein the block copolymer and the inorganic species areassembled and then the assembled inorganic species are polymerized toform a mesoscopically structured inorganic-organic composite, whereinsaid inorganic species combined with said block copolymer is a precursorinorganic species and said assembled inorganic species are hydrolyzedinorganic species, and wherein said inorganic species is a mixture ofM(OR)_(S), M(OR)_(s-t-u-v-w-y)R′_(t)R″_(u)R′″_(v)R″″_(w)R′″″_(y), and/orMX_(S) whereby: M is at least one atom other than carbon, hydrogen,oxygen, or nitrogen; S>=1 R, R′, R″, R′″, R″″, and R′″″ are organicmoieties; while 0>=s, t, u, v, w, y>=6 s-t-u-v-w-y>1; and X is a halogenatom.
 18. The mesoscopically structured material of claim 17, whereinsaid inorganic species is selected from the group consisting ofAlCl₃/SiCl₄, ZrCl₄/TiCl₄, AlCl₃/TiCl₄, SiCl₄/TiCl₄, ZrCl₄/WCl₆,SnCl₄/InCl₃.
 19. The mesoscopically structured material of claim 17wherein said inorganic species includes at least two inorganiccompounds.
 20. The mesoscopically structured material of claim 17,wherein said mesoscopically structured inorganic-organic composite hasmacroscopic orientational order.
 21. The mesoscopically structuredmaterial of claim 17, wherein said mesoscopically structuredinorganic-organic composite has a framework in which there is locatednanocrystallites.
 22. The mesoscopically structured material of claim17, wherein said mesoscopically structured inorganic-organic compositeis in the form of(a) a powder, (b) a film, (c) a fiber, or (d) amonolith.
 23. The mesoscopically structured material of claim 17,wherein said amphiphilic block copolymer and said inorganic species arecombined under non-hydrolytic conditions.
 24. The mesoscopicallystructured material of claim 17, wherein said amphiphilic blockcopolymer and said inorganic species are combined under non-aqueousconditions.
 25. The mesoscopically structured material of claim 17,wherein said block copolymer and inorganic species are assembled andpolymerized within an aligning field to form the mesoscopicallystructured inorganic-organic composite which has a macroscopicorientational order.
 26. The mesoscopically structured material of claim17, wherein said combined block copolymer and inorganic species areprocessed to induce orientational ordering before the assembledinorganic species are polymerized to form the mesoscopically structuredinorganic-organic composite.
 27. The mesoscopically structured materialof claim 17, wherein said block copolymer and inorganic species areassembled and polymerized in the presence of electrically responsivemolecules or optically responsive molecules to form the mesoscopicallystructured inorganic-organic composite.
 28. The mesoscopicallystructured material of claim 17, wherein said mesoscopically structuredinorganic-organic composite is subjected to a calcining step to form amesoscopically structured material.
 29. The mesoscopically structuredmaterial of claim 17, wherein said mesoscopically structuredinorganic-organic composite is subjected to a solvent extracting step toform a mesoscopically structured material.
 30. The mesoscopicallystructured material of claim 17, wherein said block copolymer is removedfrom said mesoscopically structured inorganic-organic composite to forma mesoscopically structured material.
 31. A product comprising any oneof(a) a catalyst, (b) a separation material, (c) a semi-permeablecoating, (d) a material for sensing an agent in a mixture that contactthe product, (e) a fuel cell material, (f) an opto-electronic material,(g) a quantum-effect material, or (h) a medical implant, the productincluding a mesoscopically structured inorganic-organic composite or amesoporous inorganic oxide material which is formed by combining anamphiphilic block copolymer with an inorganic species in a solvent,wherein the block copolymer and the inorganic species are assembled andthen the assembled inorganic species are polymerized to form saidmesoscopically structured inorganic-organic composite.
 32. The productof claim 31 formed by the following steps: placing an amphiphilic blockcopolymer in an aqueous solution of inorganic salt; combining theaqueous solution containing the block copolymer with an inorganicspecies in a solvent to form a multiphase medium that enables microphaseseparation of inorganic species and the block copolymer, thereby formingan inorganic-block copolymer composite, wherein the block copolymerenables macrophase separation of the inorganic-block copolymer compositeand the aqueous solution of inorganic salt; polymerizing the inorganicspecies to form a meso-macrostructured inorganic-organic composite;removing the block copolymer and aqueous solution from saidmeso-macrostructured inorganic-organic composite to form saidmeso-macroscopically structured material.